The co-UTOPIA of the 21st century city

1. Introduction

The city, as an expression of society and its concerns and aspirations, is always a reflection of transformations that take place, particularly in times of crises. Perhaps what differentiates this current crisis from previous ones is the speed with which these changes are occurring.

The city, understood as the space of what is public, shared and concerns us all, is experiencing moments of uncertainty - for neither the first time, nor likely the last. But this current scope of change is so great that there are those who predict the end of the city as we know it.

For this reason, and because we are ourselves also fully immersed in this transforming society, we cannot yet clearly define the destination of this transition. We cannot even say that there will be a conclusion to this period of change, which appears to bring transformation that is both continuous and permanent.

However, our social condition as human beings, with our innate desire to approach and relate to the "other", as well as our shared need to conserve our planet for the realization of a more equitable humanity, allow us to stay hopeful of what is to come. Call it a city, territory, or urban area; whatever the name, it should be built on a greater foundation of social justice and equity for its inhabitants.

2. Origin and concept

"I speak of (...) the history that understands and enables understanding (...) History answers the questions that the man of today necessarily asks himself. Explanations of complicated situations in which man will struggle less blindly if he knows their origin" (Febvre, 1970, p. 69 and 70).

Urban history always confronts us with an overcoming of the private, the home, in favour of the public, the shared space for meeting, parliament and debate. And it is precisely in this domain of the common versus the particular, where the origin of the Greek "polis" lies, which we agree to recognize as the first city in history because it defines in a practical, but also theoretical and philosophical way, the framework of urbanity.

From the beginning, the city defines two concepts. The Urbs, consisting of its physical, material, tangible dimension, which is translated into the set of buildings and their layout, i.e. the architecture of the city. And the Civitas, which comprises its social and political dimension, i.e. citizenship as a group of people associated under the same laws.

As for the Urbs, the Greek "polis" and the medieval and Renaissance cities, modelled after classical Greek cities, are cities limited to a clearly defined area, which clearly differentiate between within and beyond, and in which the center stands out from the periphery. They are cities where places (spaces) dominate over flows (movements). In the case of the Civitas, they manifest the primacy of the public over the private (home).

2.1. Historical transformations

To understand the extent of the current changes, it is useful to briefly review the behavior of cities at times of intensive transformation. Mongin (2005) defines three decisive periods in urban history that coincide with processes of globalization, that is, moments in which the city opens up to a world that is not its own, breaking its limits and overcoming its location.

The first of these occurred at the end of the 15th century. This marks when the printing press was invented, making the dissemination of ideas and the transmission of knowledge possible, which had previously been limited to monks and absolute monarchies, and it is also when new worlds were discovered, bringing new products and minerals from distant lands. The rise of markets connected merchant and maritime cities and brought about the incipient birth of banking, which was necessary to cover the costs of travel and transport. In this period, cities were still limited and contained, but networks of connections between places were already appearing. This is the beginning of flows.

The second period coincided with the first industrial revolution. The invention of the steam engine is applied to industry and to machinery for transport and communications. The development of large industries enables mass production of consumer goods and triggered the immigration of the workforce from the countryside to the city. Ships and railways revolutionize connections, electricity and the telegraph revolutionize communications. Cities grow, breaking down their boundaries and tearing down their walls. It is the extension of the urban. The residential fabric within the city is demolished, drawing new layouts and opening up wide avenues to ventilate and sanitize the dwellings. New squares and parks are created. A multitude of places appear that connect with each other and with other external places, with a consequent increase in mobility. The relevance of flows increases. Regulations and norms appear. The large number of actors involved in the creation of the city requires multidisciplinary planning. This is the birth of urban planning.

The third occurs at the beginning of the 20th century, supported by the technological changes of the second industrial revolution, the invention of reinforced concrete, the development of steel, the telephone, the electric light bulb, the internal combustion engine, the rise of the automobile, etc. The Modern Movement becomes fully involved in the improvement of society, transforming the language of architecture and the city in line with the rest of the artistic avant-gardes. Simple geometries, facades stripped of ornamentation, free floor plans and new relationships with the landscape and environment are the characteristics of a creation that aims to be mass-produced, industrially, for its democratization. The dwelling is likened to a machine whose function is to inhabit. And the city is another great machine that integrates dwellings with other artefacts, monofunctional pieces destined to work together for their efficiency. The city, according to the Athens Charter drafted at the 1933 CIAM (Congrès Internationaux d'Architecture Moderne) and published in 1942, is divided into four zones or functions: inhabiting, working, recreating, and circulating. Each of these occupies a specialized space, connected by roads that cross the city and allow fast, uninterrupted traffic away from places of residence. Road traffic is separated from pedestrian traffic, which occupies the ground level.

In these cities, there is no distinction between the center and the periphery, as each area is autonomous and independent. Medium and even high densities develop but concentrated within a few points or high-rise buildings. There is a large amount of free space between buildings, unqualified space that guarantees the entry of light and sun into residences. Hierarchization is reserved for the grid of circulation routes which are designed according to their use and specialization. It is the dominance of flows as opposed to non-existent places.

2.2. The digital era

This brief historical overview allows us to deduce that behind every significant transformation in the city, there is always a profound change in the society and world that creates and supports it. Hence, if we can know and predict these changes, we may be able to determine the fate and the characteristics of the city of the 21st century.

Undoubtedly, the great driving force of the 21st century is technological innovation. This innovation has radically changed the subjective experience of space and time. From the invention of the telephone, continuing with radio and television, and reaching the ICT of information and communication, personal relations no longer require a real space, as they can take place virtually without the need for physical presence. And time, experienced differently by each person, has ceased to be linear and is now lived in an accelerated way, one which gives priority to quantity over quality. On the other hand, the great development of means of transport has meant that spatial distance is measured exclusively in time, in the time it takes to span it, and this depends on the means of transport chosen.

Cities have become embedded in a network of highways, railways, motorways of the sea, airports and intermodal stations. The world has become full of movement, and the center has lost its attraction as opposed to the peripheries, as movements have been reversed, from inside to outside and, above all, between suburban territories. Uninhibited mobility, the pre-eminence of the communications network over the city, has led to the subjugation of urban spaces to the pressure of flows. And with this, places have been definitively displaced by flows. Consequently, new types of informal, diffuse, fragmented cities have emerged, with imprecise and confused boundaries, in an extension of the generalized urban.

In developing countries, mega-cities (formless cities) have appeared to accommodate waves of rural immigration in search of work and opportunity. They are cities that grow without history, without order, without planning.

Existing cities have grown by generating metropolis (diffuse cities), of unlimited extension, without borders; with services and headquarters in autonomous poles around them that group shopping centers, leisure spaces, workplaces and places of residence; forced by an exponential increase in mobility between suburban territories. Due to large, rapid, and disorderly growth and continuous flows, cities have become spaces that show the best and the worst. On the one hand, they offer opportunity and innovation, but on the other hand, they show segregation and marginality. In other words, cities present more serious inequalities than in the past – not only between the city and the countryside, but also between different parts of the urban area. Today’s cities house 56% of the population, consume 75% of natural resources, generate 50% of waste and emit 50% of greenhouse gases. Cities are the biggest challenge to the sustainability of the planet.

3. Changes and causes of current urban transformations

In relation to the urban transformations that today's cities are undergoing, it is necessary to highlight some changes detected at the beginning of the 21st century, which present the causes, or at least are at the origin, of these transformations. Among them, the following are worth highlighting:

3.1. POPULATION. Increase in urban demography and generational imbalance

In 2022 the world population reached 8 billion. It is expected to reach 9,709 million in 2050. Nearly 7 out of 10 people will live in cities. There is an increase in migratory movement, due to wars and ideological or religious persecution, to countries that offer resources and opportunities and to cities that must accommodate large masses of new inhabitants in a short period of time. These migrating populations suffer human rights violations in origin, transit, and destination, and produce multicultural and multiracial societies that must coexist in the same urban environment with the consequent problems of coexistence, adaptation and conflict. In host countries there is often, and especially if the influx is massive, a "fear of the other, of the different" and episodes of "intolerance of cultural and religious diversity" are generated, which seem to want to supplant "our own".

This phenomenon raises the question of whether the city can continue to be a place of welcome and coexistence for citizens of diverse origins, sharing certain values, while maintaining certain social cohesion and accepting a series of common rules; or whether it is a space of vindication that will lead to confrontations and conflicts, such as those we are already seeing in European cities. It will be necessary to RESTORE TRUST between different people, as a fundamental value, to talk about citizen strategies.

On the other hand, populations are not distributed in an even fashion. There are countries that are ageing and others that are exaggeratedly young. In some there are difficulties in caring for the elderly, in others for children and young people. In some there is a shortage of productive population and in others there is a shortage of activity. In some there is a need for labor and in others for employment. The balance of these deficits should become the driving force for the necessary INTEGRATION of different populations in common places of acceptance and welcome.

3.2. GLOBALISATION and LOCALISATION. Equal and singular

The fact that we live in an interconnected world, sharing international services of information, technology, knowledge, culture, markets, etc., located in different countries, delocalizes cities. In a globalized economy, with a shared and universalized way of life, it may seem that it has lost meaning to speak of the city in its traditional conception, in its spatial dimension differentiated from its surroundings. But although much of the city's activity is elsewhere or rather, nowhere in particular but "in the cloud", in many cases the attempt to define the essence of the city on the basis of physical, landscape and monumental attributes persists, reinforced by the pressure of the "touristification of the city".

Although there are certain global logics that provide homogeneous conditions, each city has its own history, personality, and idiosyncrasy that makes it different from the rest and makes its inhabitants proud. Contrary to the globalization that makes us equal, there is a reinforcement of identity, of what is close to us, local and in short, what makes us different.

"Globalisation does not dissolve the local, on the contrary, it creates the possibility of a much more active, much more decisive role for the local. In strictly cultural terms, places and the local are increasingly becoming trenches of identity. Faced with the general dissolution of identities in the instrumental world of the space of flows, the space of places is constituted as an expression of identity, of what I am, what I live, what I know and what I organise my life around" (Castells, 1998, p. 1).

There are no standardizable solutions, but each city has different challenges and opportunities depending on its own context. The recognition of an own IDENTITY can become a value to offer in the network of cities competing for preferential positioning in the global world.

3.3. PHYSICAL PUBLIC SPACE and VIRTUAL PUBLIC SPACE. Limited space and unlimited space

Public space is the quintessential place where citizens come together to share ideas for a common purpose. From the beginning of the history of cities as we see them, public space, referring to its physical dimension (i.e. urbs), is a spatial, material, and tangible place, which structures and orders the settlement of the city in the territory and which, referring to its social and political entity (i.e. civitas), defines the relations between its inhabitants. This second meaning is the one that prevails today because although a city is full of public spaces defined by governmental power or by disciplinary urban creation, these do not necessarily act as public spaces unless they produce collectivity. That is to say, the exercise of their purpose is determinant for their public status.

For example, the articulation of mobility networks in cities of flows attempts to reproduce urban density at certain points that we agree to call nodes. These are shopping or leisure centers, interchanges such as stations or airports, etc.... But in these places where, undoubtedly, many people meet, commercial or, at best, instrumental functions prevail. Their purpose is not to bring people together, but rather to serve purely functional purposes, often exclusively private. On the other hand, the digital society, with its capacity to form networks and links outside of a place, has altered the value of space as a support for sociability. Today, physical presence is no longer necessary to generate collectivity.

"The problem we face today is how to think about the city when we have networks instead of neighbourhoods, when homogeneous and stable space is no more than a borderline case within a global space of connected local multiplicities, when public debate has long since taken place in a virtual space, when streets and squares are no longer the main meeting and staging place. The question is whether public space, as a space of intersubjective human experience, essential to democracy, needs a kind of physical space on the Greek, medieval, Renaissance, and bourgeois model, or whether this ancient relationship between civilisation and urbanity can be realised outside the spaces of the classical European city”' (Innerarity, 2006, p.119).

Linking the physical spaces, in which public life takes place, with the virtual spaces, in which public opinion is produced, is one of the great challenges of the 21st century city in which the MATERIAL seems to be surplus to requirements in favour of the INFORMATIONAL.

"Experimenting with a new informational design of the material and a new material design of the informational seems to me to be the new frontier of urbanism" (Castells, 1998, p. 7).

3.4. PRIVATE and PUBLIC. Individual and communal

Individualization is a dominant feature of our society. We defend our freedom, we value our autonomy, and we seek our personal fulfilment, though we do not like others’ fulfilment when it interferes with our own. Even in networks, we feel empowered to the point that we expose our opinion as the "only one", without seeking to establish a dialogue that risks shaking our position. We erase tolerance and become irritated by difference, affirming what is ours as exclusive. Networks often separate us rather than communicate and unite us. Our "moral dignity" grants us endless rights without the corresponding obligation of duties. We expect gratification without the counterpart of effort and austerity. All this degrades the solidarity that we extend, at most, to family and close groups.

Life in cities is not exempt from this individualism. Citizens live in isolation, showing a lack of interest in what happens to others, attending to their immediate problems and sometimes acting under the cover of the anonymity of the masses. However, in difficult situations, such as the last pandemic caused by Covid-19, we realize that we need others and that there is a social fabric that can be trusted. Values such as solidarity, empathy, recognition of others, coexistence and acceptance of plurality and the variety of criteria emerge.

We empirically confirm that, despite being strong individuals, we are not exempt from vulnerability and that for this reason, we need the security that the group gives us. Concepts such as “neighbourliness”, association, grouping, collectivity, and so on, emerge. In short, the idea of community emerges, of "the common" that belongs to and is for everyone. Cities were born as a group of individuals united for a common purpose, subject to rules accepted and shared by the whole. Most times throughout history, they were born out of a defensive vocation, but they always turned the "common" into the essence of urban life. Now, the city will have to define whether it is only a refuge for private interests and individual needs, or whether it is a space suitable for COMMON PRACTICES.

3.5. NEW MODELS OF LIVING and WORKING

Today, people are born in one place but often live in several. Studying and learning typically happens in many others. Throughout a career, one regularly changes jobs, moving from one city to another, from one region to another country. New communication technologies make it possible to relocate workplaces. Companies work internally in networks, and network with other companies. Online work is coordinated but decentralized. Purchases are made online faster and more secure than ever before. Purchases are made from here or there, regardless of the place of origin. Leisure is consumed anywhere, no matter where it originates from. You can even attend shows virtually, taking a seat in the auditorium and experiencing the concert or performance as if you were there for real. The Internet allows us to access all these places immediately, with no waiting times or spatial barriers to prevent us from doing so. This is the effect of the globalization of space and the acceleration of time that characterizes our world.

A world that has been disrupted by new information and communication technologies and by advances in means of transport; that has been changed in such a way that almost everything is possible for almost everyone, whatever their origin, age, or condition. A world that in certain aspects has been equalized and democratized. A world in which time can be optimized and adapted to the convenience of each person; which allows family reconciliation and care for the most vulnerable; which facilitates women's access to the world of work. A world in which travel has been reduced and emissions into the atmosphere have been reduced. Plainly, a world that is potentially better.

But with new ways of life, there are aspects that contributed to the richness of social relations which have been lost and have been brought to light by the Covid-19 pandemic. Fundamentally, the natural rhythm of things has been altered and social time has been neglected. Therefore, it is necessary to recover the space of PROXIMITY and RE-HUMANIZE models to recover certain characteristics of previous models.

3.6. NEW WAYS of living and being

This changing world is reflected in society and its groups. Families, traditionally unique, have abandoned their historical concept, multiplying their typologies and promoting the coexistence of different types of family structures, perfectly valid in today's society. But there's been more than just conceptual changes; families are not stable over time, changing either because of the loss of the continuity of the nuclear family, or because of the logical evolution of the members of the group.

The dwelling, the room, constitutes the home of each of these families, so it must adjust to their variety, adapt to their tastes and ways of life and of course, be adaptable to the variations that time demands. Gone is the validity of a house forever, a house that is bought and whose continuity is intended to pass from one generation to the next, in some cases as a representation of family status. It is not even valid for a single generation that sees its members move through time and space. The dwelling has a limited life that can only be extended by being flexible, adaptable to changing circumstances. Because either it changes, or its inhabitants will change and sell it to live in another, temporarily better one. This is the reason for the rise of renting as a solution that is not tied to any location and that provides freedom and economic peace of mind in the face of changes. But this figure is subject to the laws of the liberal economy and to certain processes, such as mass tourism that invades the city centers with its purchasing power, or the purchase of housing, as a profitable investment, by firms.

Only a determined policy of public rental housing can improve this situation although, in recent times, initiatives have arisen based on co-operation, co-ownership, and co-housing, among others. These offer interesting formulas for owning as a partner, as a co-shareholder of an asset while it is being used. And when it is no longer useful for the person or family that inhabits it, this asset can be passed on, with previously agreed conditions, to another person or family that will give it a next life. Sometimes, these initiatives are also proposed as a way of exchanging services, of obtaining care, of mutuality of goods, in a collaborative lifestyle that provides interdependence in neighborhood communities that, in some ways, are reminiscent of those of yesteryear. The city of the 21st century will have to opt for a fabric of isolated, independent housing, subject to the laws and production processes of the market, or for a network of housing that supports SOCIALITY AND SECURITY.

3.7. SOCIAL AND ECOLOGICAL AWARENESS

"Urban morphology is a determining factor of quality of life because of its effects on social relations and on the lesser or greater social inequality" (Lynch, 1959).

The equality of human rights and opportunities, the acceptance of plurality, the inclusion of diversity, the elimination of physical and mental barriers, the elimination of educational, digital, conciliation and participation gaps, etc. currently, these are values that are not discussed, and which should be part of all decision-making that has to do with city planning.

On the other hand, faced with a situation of overexploitation of natural, rural and urban resources and spaces: water, soil and air pollution, reduction of biodiversity and, in effect, climate change, there is an almost unanimous awareness in favour of environmental sustainability to safeguard the planet.

The recovery of ETHICAL VALUES, efficiency and social justice, and ECOLOGICAL VALUES, the protection of the environment, is a core issue in the morphological configuration of cities that is directly linked to the traditional political aspect of urban life.

3.8. CITIZEN PARTICIPATION. New forms of governance

The governance of cities is shared between the impositions of state and supra-state governments and local governments. The former are responsible for global guidelines whose scope transcends the physical dimension of the city. They are generally rigid and distant institutions. The latter are responsible for local decisions that organize and order the functioning of the city and establish relations between its inhabitants. They are usually more flexible and closer governments that favour proximity. However, there is now a third form of government, which is the participation of citizens in local co-government.

Given the inadequacy of representative democracy, reduced to the selection of leaders, Habermas proposes "deliberative politics", which represents a model of decentralization of power aimed at achieving the levels of justice and equality that representative democracy and the market do not guarantee. Today, citizen participation is demanded not only for information and consultation on public policies but also in their deliberation and debate, in proposing new approaches and solutions, and even in making binding decisions. In this way, citizens are not simply passive recipients of government decisions, but become actors with the capacity to guide the public policies that affect them.

Thus, power can be exercised in a decentralized way, as something fluid and situational, with a variety of participants, through associations, organizations, trade unions, etc. or directly from ordinary citizens. It will be necessary to INVOLVE THE PEOPLE in decision-making to achieve a better and more liveable city.

4. The city today

The city is a complicated organism, a complex and varied system, difficult to understand in its totality. It is made up of multiple situations over time and involves a large number of actors. The preceding sections have attempted to understand it by observing it fragmentarily and arriving at partial and sometimes unconnected conclusions. However, it is necessary to combine all this data in a global diagnosis that allows us to RECOGNISE it to be able to manage it and plan its future.

If in the 20th century a rationalist model of the city was developed, centered fundamentally on the machine and its progress, in the 21st century there is a perceived need to recover the person as the center of the urban. The models of the last century must be HUMANISED, even recovering certain characteristics of previous models. But nowadays it is not enough to resort to ANTHROPO-centric models that demand respect for man, as the center of all things but rather, it is essential to work with ECO-centric patterns that understand that nature is the most valuable thing we possess, and that the preservation of planet Earth is a mission shared by humanity.

With all these clues, this second part will try to approach the city of the 21st century, a mobile and changing city whose time is so short that, possibly, it will not be possible to recognize it before its time has passed.

4.1. The PLACE of the city

Vitruvius, in his treatise "De Architectura" (15 B.C., Chapter IV, Book One), speaks of "the choice of healthy places", of the ideal location for a city, which in his vision, was in a high place with a temperate climate, far from unhealthy areas and even from the sea, as the author considered that changes in temperature and winds were harmful to inhabitants. In his conception of the ideal city, he studies the meteorological conditions of the geographical location. He attached great importance to the climate and to the sanitary conditions of the site. The city should be protected from the prevailing winds and the streets should be well oriented to the sun. For him, the safety and health of citizens is paramount.

But nowadays, it is common to see how urban planning, whether for new buildings or the growth of existing cities, ignores not only the climatic and meteorological conditions of the site but also geographical conditions such as knowledge of the terrain, topography, geology, watercourses, runoff, native vegetation and fauna, landscape, etc. It seems that today more than 2,000 years later, we have forgotten these logical lessons, and it has been the need to rationalize energy expenditure to reduce emissions that has brought us back to this vision of the city which, far from being idyllic, is urgent to safeguard what remains of our planet, without mortgaging its future or that of future generations.

The establishment of a city must consider each and every one of the factors that converge in the PHYSICAL needs of its inhabitants: light, sunshine, ventilation, health, protection, safety, security, and so on; but more than exclusively in themselves, rather by linking them to the environment.

"Environmental considerations cannot be separated from social considerations, for policy aimed at improving the environment can enhance the quality of life of citizens (...) Above all, sustainability means a better life for future generations" (Rogers, 1961, p. 32).

4.2. The SIZE of the city

In the face of the expected population explosion in cities, the question arises as to whether the city has an optimal size or whether it can grow indefinitely.

"Each thing, in order to possess all the properties proper to it, must be neither inordinately large nor inordinately small, because, in that case, it has either completely lost its special nature, or it has become perverted (...) The same is true of the city: too small, it cannot satisfy its needs, which is an essential condition of the city; too large, it is sufficient for itself, but not as a city, but as a nation, and government is hardly possible in it" (Aristotle, 330-323 B.C., Book IV, Chapter IV).

Aristotle argues, therefore, that the size of the city lies between the lower limit of its AUTONOMY and the upper limit of its GOVERNABILITY. That is, between the capacity for all citizens to live as "free and sober men" and the political capacity to maintain an internal order to manage it.

If one of the principles of the 21st century is EQUITY AND SOCIAL JUSTICE, the city must provide all its inhabitants with equal, and if not identical at least similar, living conditions. Therefore, there is no room for dimensions or schemes that segregate part of the population, leaving them outside the minimum vital services. There is no room for solutions that do not integrate the entire population, native or migrant, avoiding situations of lack of protection or inferiority. In short, circumstances that aggravate the social distance between some groups and others are not acceptable.

Nowadays, we are far removed from utopias for which it would be easy to determine, in drawing or writing, the ideal city and which would be suitable for any time and place. Despite globalization, the complicated economic and social reality of each territory means that solutions that are favourable for some cultures and sizes are harmful for other societies and dimensions. Consequently, it is difficult to choose one size of city over another.

"In fact, the great variety of city sizes present in the real world calls into question the very existence of an optimal size, which could vary from one country to another and even from one city to another, also taking into account the specialisation of each city in terms of the theory of central places, or more recent approaches such as urban networks" (Camagni, 2013, cited by Jiménez Romera, 2015, p. 26).

The focus of interest is therefore not the optimal size, but the efficiency of different sizes depending on the urban form and productive structure of each city. It seems more logical to opt for the objective of balanced growth and a strategy that avoids congestion and conflicts.

4.3. The STRUCTURE of the city

At present, the growth of cities is torn between a continuous and dense fabric and a discontinuous urbanization, less dense and more dependent on mobility than on proximity to central areas. Apparently, the first solution allows for low-intensity, public or pedestrian-cyclable mobility, more in line with the sustainable city we advocate. Moreover, "concentration facilitates social interaction, diversity as a source of creativity, human capital and local synergies as sources of learning and the attractiveness of urban services and facilities" (Camagni et al., 1993, cited by Jiménez Romera, 2015, p. 25).

However, it is difficult for this type of cities to be isotropic, that is, equivalent in all directions and places in space, so that the different proximity to the center and to services, measured in terms of distance or travel time, creates social differences that are radically contrary to the principle of equity. While in Europe urban centers push the less affluent classes to the peripheries, in the United States urban centers remain in the hands of the economically weaker classes. In any case, a mosaic emerges whose parts are increasingly different, in social and economic terms.

On the other hand, when distances in cities that are growing as "oil blotches" increase, it is necessary to organize mobility according to the different means of transport and their speed. Within the city,

"a series of avenues or main roads emerge that channel the fastest traffic. The new avenues constitute privileged routes through the city, but at the same time they become barriers that hinder transversal movement, because such speeds are largely obtained by reducing the number of crossings and intersections. In this sense, ring avenues may seem an opportune solution to avoid congestion in central areas, but (...) they pose a future barrier to the connection of new city expansions with central areas" (Piccinato, 1974, cited by Jiménez Romera, 2015, p. 15).

These cities are more efficient, due to their concentration and density, but they are hierarchical, far from the homogenization of the pursued principle of equity, they have difficulties of connectivity between the parts and growing mobility problems depending on the size of the city. They work well in small and even medium-sized towns, where public transport is the best option for getting around, assisted by pedestrian-cyclable transport, with restrictions on private cars, and where services are balanced by zones or neighborhoods.

The second type, the city as a set of towns or poles, interconnected through the road network, avoids the concentration of infrastructures in the historic center, while the relatively regular transport network generates a fairly isotropic territory in terms of accessibility. This decentralization implies the homogeneity of the territory, both in terms of essential services and general infrastructures. These are cities that free themselves from the center, but at the cost of losing their identity.

"The generic city is the city freed from the captivity of the centre, from the straitjacket of identity. The generic city breaks with this destructive cycle of dependence, it is nothing but a reflection of the current need, of the current capacity. It is the city without history. It is big enough for everyone. It is comfortable. It is maintenance-free. If it gets too small, just expand it. If it gets old, it simply self-destructs and renews itself. It is just as exciting (or not exciting). It is as shallow as a Hollywood film studio. It can produce a new identity every Monday morning" (Koolhaas, 1995, p. 1.6).

These cities seem to move away from the traditional concept of the city as a place of agreement and coexistence that forges identity. They seem to be dominated more by the need to move than to meet. However, they have characteristics that are more in keeping with modern life and thinking. They are homogeneous and balanced, they have no limits as they grow or shrink without trauma, they have no historical ties, they renew themselves without complexes, they accept everything and everyone. In short, they are FREE to be what they want and when they want. Their biggest problem is the increase in mobility, with the consequent cost in lost time and ecological price, and the danger of degradation of the empty territories between populations that Koolhaas dares to describe as "garbage space". This type of city works well in medium-sized or even large towns, where transport is entrusted to suburban trains or the metro, with limited use of the private car, and where services are compensated by zones or neighborhoods.

Currie (1976), in the framework of the "United Nations Habitat Conference", speaks of "cities within cities" to order the unstoppable urbanization of cities in developing countries. In any case, both in the dense city and the more dispersed city, we share this idea since, depending on the culture of the place and the productive conditions of its society, either of the two schemes can be valid if adequately and appropriately planned. In both cases it is a matter of pursuing POLYCENTRIC cities, with a certain DENSITY, whose centralities are self-sufficient basic units in which everything is mixed, housing, services, facilities, public spaces, commerce, and work. The aim is to achieve harmonious development and a high degree of autonomy to satisfy the usual and basic needs of all the citizens who occupy them and who will only have to move around in special situations. They can be called neighborhoods in the compact city, or urban communities in the more dispersed city. But all of them, by sharing a spatial area, must promote proximity relations to achieve urban integration. They must go beyond a mere instrumental organization by trying to forge IDENTITIES that are relatively homogeneous and provoke a sense of belonging that unites the community.

What will change in some types of cities or others, is the way in which the basic units are linked, varying between tangential ones that share boundaries, those linked by lines or those integrated in a networked mesh. The type of linkage will determine the movements which, as has been said, should be minimized, prioritizing public services over private ones, and limiting them to the achievement of extraordinary services.

4.4. USES in the city

In today's society, changes are so rapid that rigid formalizations and watertight compartments are no longer valid. Everything must be mobile, adaptable to last over time, and FLEXIBLE enough to be able to serve diverse users and changing technologies in continuous development.

"Today, the major concern in our social and individual life is to prevent things from becoming fixed, so solid that they cannot change in the future. We don't believe that there are definitive solutions, and not only that: we don't like them" (...) What does it mean to be flexible? It means that you are not committed to anything forever, but ready to change the tuning, the mind, at any time it is required. This creates a liquid situation. Like a liquid in a glass, where the slightest push changes the shape of the water" (Bauman, 1999).

After the failure of the zoning by uses advocated by the Modern Movement and the CIAMs, it is clear that the modern city must be configured on the mix of uses, without which the autonomy of the parts, defended in the previous point, is not possible. But mixing is not enough; it is also necessary to HYBRIDISE them. Places to live and to work, to learn and to play, to eat and to meet, as a library and a museum, to do sport and to watch shows or to do theatre, etc.

The definition of areas can no longer be "one size fits all" but must be open and flexible enough to adapt to different demands. It is as if architecture exchanges its Vitruvian characteristic of solidity ("firmitas") for LIQUIDITY.

"Liquids have no defined form, they are sensitive to transformation. They are not supported and their support defines them by containment. They are malleable and mobile. They are in an intermediate state between solidity and evaporation. They are imprecise and incomprehensible. Their molecules take random shapes that vary over time. Solids tend to remain, while liquids tend to pass away" (Ito, 2006).

Liquidity, in turn, leads to the progressive dematerialization of an architecture that feels ephemeral and, therefore, freed from its transcendence. Architecture no longer has the will to last in time, as in the past, but to serve its time. And that is why it allows itself to be "participated in" by the user, it allows itself to be "used" in every event, without fear of continuous change.

4.5. The LIMITS of/in the city

"In Japan, when the cherry blossoms bloom, we gather under their branches to celebrate. By means of elongated curtains, we separate the space, which then becomes a place of celebration during the ceremony, only to return to nature after the ceremony. In my opinion, there is no better architecture" (Ito, 2006).

The limit of the city, of architecture itself, has ceased to exist. Something as ephemeral as a few simple curtains temporarily delimit a place for an event, transforming it for the celebration of spring. It is the experience of that space, at that specific moment, that turns it into architecture and temporarily separates it from nature. Sheets, membranes, skins, fabrics, canvases replace walls and enclosures in an architecture that merges, merges with the landscape, whether urban or rural. And the limits become imprecise, light, changing in a DIFFUSE definition of what is inside and what is outside.

At the edges, the sense of inside is lost and the outside is felt, borders become moldable, the boundary is lost. But this does not happen exclusively at the edges of the city where the transit of "going out and coming in" is no longer felt, but also in the interior, in the urban proper, where the limits become blurred and the uses, public and private, merge and become confused in a new definition of the same. The private takes place in spaces outside the home, the city appropriates part of its functions. People sleep in hotels and shelters, eat in restaurants, or buy food in the street, use public services and toilets, spend their free time and rest in recreational places outside the home.

On the other hand, at home, people work, socialize, share, heal, take care of themselves... The uses overlap, while the intimate goes outside, the public comes inside in a fusion that redefines the concepts of home and city. Ito (1985-1989) asks, with regard to his PAO dwelling for the nomadic girl in Tokyo, "what is a house for her (...) The concept of house for her is scattered all over the city and her life goes by as she uses the fragments of urban spaces as a collage".

4.6. The PLACES of the city

ICTs, new information and communication technologies, play an important role in this redefinition of concepts. If the boundaries are blurred between the real, intertwining private and public functions, they are even more blurred between the real and the virtual. Today, knowledge is not only produced in specific places but extends to the internet and its applications. Information is no longer communicated exclusively on physical media, but increasingly on digital media. Social relations emerge in both physical and virtual scenarios.

Today, physical presence is no longer a prerequisite for social interaction. In the virtual world, distance has disappeared, and space has been reduced to one. Time has abandoned its linear and progressive condition, turning before and after into a series of repetitions without the need for temporal location. In the virtual world does not exist in either differentiated space nor time.

There are those who warn of the risk that the digital society, with its links to the margins of a place and a history, will destroy the value of space as a support for sociability, that it will do away with the distinction of the local in the face of the uniformity of the global. However, although it is undeniable that ICTs create new tools that have a direct impact on urban processes and on social relations and practices, experience shows that they also produce novel interactions in the generation of encounters between people. Networks make it possible to connect people, whether known or unknown, foster relationships between activities in different geographical contexts, and facilitate unthinkable encounters between strangers. Many of these contacts do not cross the frontiers of the virtual world, but others, on the other hand, materialize in the real world. Both worlds, virtual and real, feed off each other, constructing permeable frontiers which, in this case, do not respond to physical limits.

Ito's 'The Nomadic Girl in Tokyo' (1985-1989), gets rid of everything that is not indispensable for living but keeps an "intelligent piece of furniture, a device for placing and storing the apparatus destined to obtain information about what is happening in the city and store it". It is an information capsule to navigate the city, to move around, to modify routines, to feel safe anywhere, to find people to socialise with, to form groups to act with. And all of this in real time.

A HYBRIDISATION between the physical and the virtual thus appears as a support for sociability that endows public space with new content.

"The idea of connecting activity with memory, of connecting flows with places... experiencing with a new informational design of the material and a new material design of the informational seems to me to be the new frontier of urbanism. How to make an informational city a city" (Castells, 1998).

The success of the public space of this informational city does not depend so much on a physical design that structures and structures the city, on ornamental attributes that embellish it, but on its capacity to house and promote activities. It must therefore be multifunctional, adaptable and, above all, capable of attracting people and generating life because "life in a city is self-reinforcing: something happens, because something happens because something happens" (Gehl, 2010).

4.7. The INHABITANTS of the city

Urban regeneration policies, while necessary, have had consequences that severely affect the population of cities. Land price speculation and the gentrification of these urban centers exclude a large part of the population. The search for investment to strengthen local economies has meant that citizens have been relegated to the background, supplanted by tourists, occasional residents, and transient residents. Facilities are sometimes designed more to attract investment than to serve permanent citizens. And all this aggravates inequalities by affecting a fundamental problem: accessibility to housing.

Who is the inhabitant of today's city, the city open to the world, smart-ised, seeking a competitive position in the global world in which we move, who is the inhabitant of the city that fights to preserve, or seek, a local identity in which they recognise themselves as individuals and as a group, who is the inhabitant of the city that grows without limits and must welcome men and women from different countries, different cultures and multiple economic, cultural and social situations?

It is difficult to define this inhabitant in a free society which, by definition, cannot exclude anyone. Thus, it is easier for the inhabitant to exclude himself. Because an inhabitant will not be such if he does not want to be one, if he has no sense of community, if he does not feel capable of respecting others and, in short, if he does not collaborate in the construction of his "CITY".

In the same way that the right to work, to education, to health, to housing, to leisure and to life is indisputable today, there is the right to the CITY, to urban life, to meeting places and exchanges, to the full use of collective places, for everyone. Because the city is first and foremost a collective, and therefore community interests will always take precedence over those of the individual.

Its design must prioritise the HUMAN dimension, putting the needs of the people who use it and live in it before everything else. It is unacceptable for streets to be considered interstitial spaces whose main purpose is the circulation of private vehicles. It is unacceptable that their surfaces be partly used for permanent car parking, depriving pedestrians of the possibility of walking on wide pavements, when these are linked to the ground floors of buildings occupied by local businesses, where it is possible to take a leisurely stroll and meet neighbors. Noise and pollution levels that make people ill cannot be allowed. It is unacceptable that its section does not allow the sun to shine on the houses that flank it or on the trees that try to shade their living areas.

Making the city a vital place, the scene of multiple human relationships is the first condition for the regeneration of cities. "Living cities have wonderful innate capacities to understand and communicate, to devise and invent what is necessary to combat their needs (...) Inert and lifeless cities usually contain the germs of their own destruction and little else. By contrast, cities of intense, lively and diverse life contain the seeds of their own regeneration and have the energy to take on problems" (Jacobs, 1961).

Making the city a safe place, but not coercively or repressively, but "thanks to a dense and almost unconscious network of controls and reflexes of voluntariness and willingness inscribed in people's minds and constantly nourished by them" (Jacobs, 1961) alludes to informal surveillance mechanisms coming from street users, proposing to empower them as opposed to assigning this function to the police. Securing "the eyes of the street", with a large influx of pedestrians, ensures permanent supervision.

Make the city a healthy and sustainable place.

"Cities themselves should be conceived as ecological systems and it is this attitude that should drive our approach to planning them and managing the exploitation of their resources. The resources consumed by a city can be measured in terms of the ecological footprint they leave behind (an area scattered around the world, larger than the city limits on which it depends) (...) The ecological footprints of cities already cover virtually the entire planet. ...Their expansion is occurring at the same time as the erosion of fertile lands, seas and virgin rainforests" (...) "given this limitation of livelihoods, the dramatic effect on ecology of urban layouts must be reduced and circumscribed" (Rogers, 1966, p.30).

Making the city an inclusive and accessible place. "The city belongs to everyone (...) the city has universal value as a meeting place where people share common interests (...) it has value because of the people who inhabit it (...) it is a place that disallows selfish lifestyles" (Mendes da Rocha, 2011, p.13).

4.8. The CREATION of the city

Making a city is a collective task that requires political, technical and citizen collaboration. Firstly, there must be a "strategic model" that develops over time in response to the problems and needs that arise. Given that urban planning processes are slow and cannot typically keep up with the speed of changes, such a model must have a certain flexibility to avoid the risk of solutions becoming outdated and inefficient before they are even implemented. However, as achieving a given type of city relies on developing fundamental strategies for its planning and development, the intended outcomes of the model should be robust. It also goes without saying that these plans should be ambitious, so as to maximize the improvement of citizens’ quality of life and interpersonal relations.

The definition of the model is a task for civil and governing bodies, particularly for local politicians democratically elected for this mission, among others. But the responsibility does not exclusively fall on them, as citizens will have to contribute opinions, propose improvements that relate to their experiences, and hold politicians and their work accountable to collective expectations and electoral promises they have made.

On the other hand, as has been explained throughout this manuscript, there are decisions that transcend the local level to form part of the global component that characterizes this era we live in. Guidelines from the United Nations, other international organizations, supranational governments, or even certain NGOs must be followed, so long as these seek to prioritize the common good and the preservation of the planet. Given the multidisciplinary nature of urban planning, the development of the "strategic model" will incorporate professionals from different fields of knowledge who will contribute their analyses and visions of the city's problems. In addition to architects and engineers, historians, geographers, landscape architects, biologists, psychologists, sociologists, economists, jurists, etc. will be needed. And, once again, the ACTIVE PARTICIPATION of citizens will be required, both individually and through associations, to share and validate, or not, the decisions that are made. And it is precisely the incorporation of citizens in these free and inclusive participation processes, in each and every phase, that is the novelty of the ideation and creation of the city of the 21st century.

"Creative citizenship entails participation in essentially creative community activities. It energises communities; it may fill vital gaps in many purposeless lives; it provides social prestige, satisfaction and identity; and it addresses the causes of much of the disharmony and alienation in society..... In the long term, the social, environmental and economic benefits of this kind of civic work could transform patterns of urban life. We have seen the development of our cities as strictly the responsibility of the public and private sectors separately, and the post-industrial city requires the participation of all citizens. Deploying the labour energy of the unemployed, the untapped faculties of the young and the experience of adults to solve problems ignored by the public sector and by a purely performance-driven private sector would be a decisive collaboration to replace poverty, dependency and alienation with equality, initiative and participation" (Rogers, 1966, p.150).

Involving citizens in the process of growth and improvement of their cities should not be limited to simply informing them about the evolution of the different phases of planning. Instead, it should also involve consulting their opinion and even decision-making capacity.

4.9. The MANAGEMENT of the city. New TECHNOLOGICAL tools

City planning must be aimed at achieving a "strategic model" that is established and shared by policymakers and citizens. This model is never finite nor finished but develops and progresses over time. The model must be modifiable in response to events, adaptable to changes of the citizens and groups that it concerns. To achieve the established project, is essential to have clear objectives and outline strategies that lead to their completion based on the values that each city possesses. Furthermore, it is crucial to manage the available resources well. Resources of all kinds (natural, climatic, landscape, artistic, material, energetic, business, endowments, etc.) must be aligned to serve the collective aspirations outlined in the vision of the future.

To this end, the latest TECHNOLOGIES of the DIGITAL era are of great help in the management and continuous improvement of the city. But it must be understood that technology has an exclusively instrumental application in the case of urban planning. It is a tool at the service of the management of the city and the scope of its values. Among the technologies available and currently in use several can be highlighted, each addressing different purposes:

In relation to strategies for the location and positioning of cities and their growth. The Geographical Information System (GIS) is used. This tool works with geo-referenced information that analyses the spatial location and organizes layers of information in different visualizations, using maps, reports, graphs, 3D scenes, etc... Obtaining this complex topographic and meteorological data helps form location guidelines that seek to improve the comfort and safety of inhabitants, the efficiency of water and energy consumption and the rationality of travel networks. With them, it is possible to learn which lands are at risk of floods or fires, in seismic danger, their landscape or artistic value, and so on.

In relation to obtaining data in real time. Incorporating agile management and governance mechanisms with dynamic legislation and policies that are flexible and adaptable requires continuous and real-time data to be collected. Today, this is possible by collecting data from a wide range of sources, such as from the Copernicus satellite, the national statistics institutes and other official bodies to data that can be provided by private companies. City datasets have different scales and are mobile over time, dynamic and sometimes vary at very short intervals. Moreover, they are synchronous change at different speeds. Today's urban planning makes use of partial layers of information which, when combined and superimposed, can generate more complex insights than when considered individually. The mapping of datasets, their interrelation, their collection in real time and their synchronization are today fundamental for effective decision-making in time and place.

In relation to the construction of flexible, easily modifiable models. In architecture, the Building Information Modelling (BIM) work methodology is used which consists of making a "model", a virtual copy of an existing or future building and describing all its characteristics. This “model” can then be used to evaluate the impact of different actions or decisions on the real building before these are implemented, enabling a more informed decision-making process. BIM creates digital representations of multidisciplinary data, which are then uploaded to a cloud platform to allow real time collaboration between multiple parties. Each professional can, from their own place of work, form part of a delocalised team that introduces data to the model and contributes their various ideas, visions, and knowledge. The model allows interferences, incompatibilities, frictions, and collisions to be detected, so that potential conflicts can be resolved before they occur in reality.

City Information Modelling (CIM) is the application of BIM to cities. Although it is associated with the same concept, it uses a more sophisticated platform so that planners, engineers, designers, and architects can work together on the design of cities as if they were projects. Information is the core of the methodology of both BIM and CIM, and making it available to everyone eliminates silos, as well as reducing costs and time, thus democratizing knowledge of the project and enabling collective decision-making. In this sense and focused on cities, CIM can equip smart cities with a collaborative work tool, in terms of design, that facilitates the integration of urban services and the participation of citizens in city transformation. CIM can improve a city’s efficiency, share information with the public, facilitate higher quality services, ensure the wellbeing and safety of citizens, and guarantee the optimal use of resources, thus minimizing waste and environmental impact.

In relation to the functioning of cities. But the real opportunity that BIM and CIM offer is the possibility of integrating city planning interactively with artificial intelligence systems (through platforms such as BIM Internet of Things) or with land management (through BIM GIS software). These links can help cities create intelligent connections between buildings and infrastructures (such as the transport system, public services, communications, energy consumption, etc.) and achieve a centralized and efficient management of public services. Computerized modelling or simulation of models in BIM and CIM, which reflect the complex matrix of criteria that make up the modern city, can measure the impact of strategies on a variety of considerations, such as natural light usage, energy efficiency over days or seasons, the needs of pedestrian and vehicular movement, and parking demand, among others.

In relation to citizen participation. In the present day, participation in the city is easy thanks to participation platforms, which are open and collaborative networked digital spaces that connect policymakers and citizens in the search for participatory governance. These platforms enable open management, a new type of governance, in which citizens have the ability to stay informed, as well as monitor and intervene in the life of their city.

5. Conclusion

The advent of digital technologies has sparked an epochal change in the history of humanity. The possibility of online communications has brought about a real revolution in human relations. Now, it is not only possible to connect physically; but rather, one can do so irrespective of the place or time in which the communicating parties are located.

This possibility means a real transformation in the world of work, in every sector. In the personal world, as work can be carried out online by connecting internally with our company or externally with others on the market; in the commercial world, as any product is within the reach of any buyer in a short time; in the world of culture, as it is possible to attend any event in real time or in playback; in the world of information, as it is available in its entirety in across the world; in the world of communication and participation, as it is possible to give opinions and share visions with different groups and users.

But the most revolutionary aspect of these new technologies is that notions of space and time have been completely altered. While space has shortened, time has expanded. Physical distance and human time have ceased to be real, with the former shrinking and the latter enlarging. Since it is no longer necessary to travel long distances to meet each other, movements are reduced, and as we do more in less time, we have more of it to spare.

Now emerges the opportunity to tend to PROXIMITY, to the lost social relationships that humanize us, the personal exchanges that bring us happiness and the leisure activities that give us pleasure. It is the time of a return to principles, of return to PLACES. The paradox is that this return to places is made possible by the increase in flows, on whose assistance and supply we depend. In this return, humans replace machines to become once again the centre of the urban and nature accompanies us in this resurgence of care for the planet. Everything is once again measured in relation to the PERSON, to their wellbeing.

In the 21st century, cities will have to project the micro, the user, onto the macro, the city. Among the micro will be the PLACES that will serve as a free and spontaneous meeting place for inhabitants, foster social interaction, create links between the population and contribute to forging a common IDENTITY and awareness. Macro will include FLOWS, connections, communications, networks, and everything that contributes to a good POSITIONING in the global world.

The unlimited extension of large cities, which grow without end, will require a subdivision into SMALLER sizes, so that the inhabitants can live fully as "free men", in cities made to measure, with a human scale that is nothing other than "the relationship of our body with the environment that surrounds it" (Pallasmaa, 1996).

Cities, however large, should develop POLYCENTRIC models, which "integrate communities within neighbourhoods and optimise their proximity" (Rogers, 1966), and which serve their population with comprehensive and nearby services. However, they may vary in the way they link these centres, provided that, in compliance with the principle of EQUITY, the networks they form are balanced, with horizontal relations between their components - that is, absent of hierarchies. The rest will depend on the "genius loci", on the culture of each place.

Cities will be DENSE and COMPACT, at least enough to guarantee exchange between different citizens, who form a "community", and the efficient management of resources. But, at the same time, they will be PERMEABLE, open to cross-connections that prevent the abandonment of any part of the city.

They will forget the fragmentation of modernity, proposing a mixture and coexistence of uses that guarantee the variety of activities, the mix of population and the inclusion of cultures. They will be COMPLEX AND DIVERSE, as differences will be understood as a value that adds, rather than subtracts, opportunities. And they will be SAFE, as coexistence and encounter produce security.

Cities, to survive over time, will be FLEXIBLE, moving in a calculated vagueness that allows them to change, modify their objectives, and progress. Their boundaries, both internal and external, will be DIFFUSE, sensitive to transformation. Cities will tend not to CONTINUE but to SERVE.

Cities will need to be AWAKE to recognise their values and realise their potential. They will be CREATIVE and agile enough to emerge from their opportunities or their failures, because progress will always translate into opportunity for their inhabitants. And they will do so aided by their TECHNOLOGICAL features, with access to services, energy, information, transport, networks and any other technological, information or knowledge innovation that the future can provide.

Cities will emerge adjusted to their ECONOMIC viability, according to their possibilities and resources. But they will never forget ENVIRONMENTAL sustainability, which will oblige them to minimise their ecological impact, reduce their energy consumption, improve their mobility, and provide efficient and safe solutions in their infrastructure. Nor will they abandon the goal of SOCIAL sustainability that will demand universal access to all services and equal treatment for all citizens, regardless of where they come from, the religion or culture they profess, their physical or intellectual characteristics, their gender or age.

Making these cities will be no easy task. The integrated knowledge of experts, whether professional architects, engineers, sociologists, psychologists, topographers, geographers, or historians, will not be sufficient. The ideas of local leaders and the global policies of official bodies will not be enough. Naturally, private intervention initiatives will not be enough. None of this will be enough for cities to be born and develop as living organisms that change and evolve without losing their relevance and becoming obsolete in short intervals of time.

What will make this possible is the ACTIVE PARTICIPATION of citizens, who will have to be listened to by public and private entities in their search for a city that builds a balanced and varied landscape; to be attended to in their right to decent housing; to be considered in their need for services; to be responded to in their search for opportunities; to be united in an identity in which they recognise themselves as a community.

In short, the city of the 21st century will emerge from a new form of governance, co-GOVERNANCE, which knows how to exploit modern technologies and assimilate the dynamic complexity of the modern city, involving a society in which new values such as con-SERVATION as opposed to expansion are emerging, re-UTILISATION as opposed to renovation, co-OPERATION as opposed to competition, sharing as opposed to sharing out and, above all, co-LABORATION in the construction of a possible co-UTOPIA for the maintenance of everyone's planet and the achievement of a more integrating and equitable city for all, THE CITY OF THE 21st CENTURY.

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