Artículos con la etiqueta ‘ciudades’

Zipf’s Law for All the Natural Cities around the World

Por • 13 feb, 2014 • Category: sociologia

Two fundamental issues surrounding research on Zipf’s law regarding city sizes are whether and why Zipf’s law holds. This paper does not deal with the latter issue with respect to why, and instead investigates whether Zipf’s law holds in a global setting, thus involving all cities around the world. Unlike previous studies, which have mainly relied on conventional census data, and census- bureau-imposed definitions of cities, we adopt naturally and objectively delineated cities, or natural cities, to be more precise, in order to examine Zipf’s law. We find that Zipf’s law holds remarkably well for all natural cities at the global level, and remains almost valid at the continental level except for Africa at certain time instants. We further examine the law at the country level, and note that Zipf’s law is violated from country to country or from time to time.

How a New Science of Cities Is Emerging from Mobile Phone Data Analysis

Por • 30 ene, 2014 • Category: sociologia

Study the way people make mobile phone calls in metropolitan areas and you can see a city breathe, say computer scientists. Mobile phones have generated enormous insight into the human condition thanks largely to the study of the data they produce. Mobile phone companies record the time of each call, the caller and receiver ids, as well as the locations of the cell towers involved, among other things. The combined data from millions of people produces some fascinating new insights in the nature of our society. Today, computer scientists have gone one step further by using mobile phone data to map the structure of cities and how people use them throughout the day. “These results point towards the possibility of a new, quantitative classification of cities using high resolution spatio-temporal data,” say Thomas Louail at the Institut de Physique Théorique in Paris and a few pals.

Universal Predictability of Mobility Patterns in Cities

Por • 30 jul, 2013 • Category: sociologia

Despite the long history towards modeling human mobility, we continue to lack a highly accurate but low data requirement approach to predicting mobility patterns in cities. Here, we present a conduction-like stochastic process without adjustable parameter to capture the underlying driving force accounting for human mobility patterns at the city scale. We use various mobility data collected from a number of cities with different characteristics to demonstrate the predictive power of our model, finding that insofar as the spatial distribution of population is available, our model offers universal prediction of mobility patterns in good agreement with real observations, including distance distribution, destination travel constraints and flux. In contrast, the models quite successful in modeling mobility patterns in countries are not applicable in cities, suggesting the diversity of human mobility at different spatial scales. Our model has potential applications in many fields relevant to mobility behavior in cities, without relying on previous mobility measurements.

Space-time correlations in urban sprawl

Por • 23 jun, 2013 • Category: Economía

Understanding demographic and migrational patterns constitutes a great challenge. Millions of individual decisions, motivated by economic, political, demographic, rational, and/or emotional reasons underlie the high complexity of demographic dynamics. Significant advances in quantitatively understanding such complexity have been registered in recent years, as those involving the growth of cities [Bettencourt LMA, Lobo J, Helbing D, Kuehnert C, West GB (2007) Growth,. Innovation, Scaling, and the Pace of Life in Cities, Proc Natl Acad Sci USA 104 (17) 7301-7306] but many fundamental issues still defy comprehension. We present here compelling empirical evidence of a high level of regularity regarding time and spatial correlations in urban sprawl, unraveling patterns about the inertia in the growth of cities and their interaction with each other.

The Origins of Scaling in Cities

Por • 23 jun, 2013 • Category: sociologia

Despite the increasing importance of cities in human societies, our ability to understand them scientifically and manage them in practice has remained limited. The greatest difficulties to any scientific approach to cities have resulted from their many interdependent facets, as social, economic, infrastructural, and spatial complex systems that exist in similar but changing forms over a huge range of scales. Here, I show how all cities may evolve according to a small set of basic principles that operate locally. A theoretical framework was developed to predict the average social, spatial, and infrastructural properties of cities as a set of scaling relations that apply to all urban systems. Confirmation of these predictions was observed for thousands of cities worldwide, from many urban systems at different levels of development. Measures of urban efficiency, capturing the balance between socioeconomic outputs and infrastructural costs, were shown to be independent of city size and might be a useful means to evaluate urban planning strategies.

The hypothesis of urban scaling: formalization, implications and challenges

Por • 29 ene, 2013 • Category: sociologia

There is strong expectation that cities, across time, culture and level of development, share much in common in terms of their form and function. Recently, attempts to formalize mathematically these expectations have led to the hypothesis of urban scaling, namely that certain properties of all cities change, on average, with their size in predictable scale-invariant ways. The emergence of these scaling relations depends on a few general properties of cities as social networks, co-located in space and time, that conceivably apply to a wide range of human settlements. Here, we discuss the present evidence for the hypothesis of urban scaling, some of the methodological issues dealing with proxy measurements and units of analysis and place these findings in the context of other theories of cities and urban systems. We show that a large body of evidence about the scaling properties of cities indicates, in analogy to other complex systems, that they cannot be treated as extensive systems and discuss the consequences of these results for an emerging statistical theory of cities.

Universities Scale Like Cities

Por • 23 nov, 2012 • Category: sociologia

Recent studies of urban scaling show that important socioeconomic city characteristics such as wealth and innovation capacity exhibit a nonlinear, particularly a power law scaling with population size. These nonlinear effects are common to all cities, with similar power law exponents. These findings mean that the larger the city, the more disproportionally they are places of wealth and innovation. Local properties of cities cause a deviation from the expected behavior as predicted by the power law scaling. In this paper we demonstrate that universities show a similar behavior as cities in the distribution of the gross university income in terms of total number of citations over size in terms of total number of publications. Moreover, the power law exponents for university scaling are comparable to those for urban scaling. We find that deviations from the expected behavior can indeed be explained by specific local properties of universities, particularly the field-specific composition of a university, and its quality in terms of field-normalized citation impact.

Modeling Spatial Equilibrium in Cities: the Isobenefit Lines

Por • 3 nov, 2012 • Category: sociologia

I propose and briefly define the concept of Urban Isobenefit Lines by using functions as easy as efficient, whose results can offer a rich tool to use into spatial equilibrium analysis involving cities. They are line joining urban points with equal level of positional advantage from city amenities. The results which one obtain by implementing a chosen function, gave specific scenarios: numerically described by indicators and graphically visualized by efficient city matrix views. This is also a theoretical concept for the Urban Economics theory and Spatial Equilibrium analysis in cities.

Professional diversity and the productivity of cities

Por • 1 nov, 2012 • Category: sociologia

The relationships between diversity, productivity and scale determine much of the structure and robustness of complex biological and social systems. While arguments for the link between specialization and productivity are common, diversity has often been invoked as a hedging strategy, allowing systems to evolve in response to environmental change. Despite their general appeal, these arguments have not typically produced quantitative predictions for optimal levels of functional diversity consistent with observations. One important reason why these relationships have resisted formalization is the idiosyncratic nature of diversity measures, which depend on given classification schemes. Here, we address these issues by analyzing the statistics of professions in cities and show how their probability distribution takes a universal scale-invariant form, common to all cities, obtained in the limit of infinite resolution of given taxonomies.

Distance weighted city growth

Por • 21 sep, 2012 • Category: sociologia

Urban agglomerations exhibit complex emergent features of which Zipf’s law, i.e. a power-law size distribution, and fractality may be regarded as the most prominent ones. We propose a simplistic model for the generation of city-like structures which is solely based on the assumption that growth is more likely to take place close to inhabited space. The model involves one parameter which is an exponent determining how strongly the attraction decays with the distance. In addition, the model is run iteratively so that existing clusters can grow and new ones can emerge. The model is capable of reproducing the size distribution and the fractality of the hull of the largest cluster. While the power-law distribution depends on both, the imposed exponent and the iteration, the fractality seems to be independent of the former and only depends on the latter.