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    ABSTRACT: Bicycle sharing systems (bike-shares) are becoming increasingly popular in towns and cities around the world. They are viewed as a cheap, efficient, and healthy means of navigating dense urban environments. This paper is the first to take a global view of bike-sharing characteristics by analysing data from 38 systems located in Europe, the Middle East, Asia, Australasia and the Americas. To achieve this, an extensive database depicting the geographical location and bicycle occupancy of each docking station within a particular system has been created over a number of years to chart the usage in the chosen systems (and others) and provide a consistent basis on which to compare and classify them. Analysis of the variation of occupancy rates over time, and comparison across the system’s extent, infers the likely demographics and intentions of user groups. A classification of bike-shares, based on the geographical footprint and diurnal, day-of-week and spatial variations in occupancy rates, is proposed. The knowledge of such patterns and characteristics identifiable from the dataset has a range of applications, including informing operators and policymakers about the maintenance of a suitable balance of bicycles throughout the system area (a nontrivial problem for many bike-shares), the location of new docking stations and cycle lanes, and better targeting of promotional materials to encourage new users. Within the context of transport research, the systems utilised here are part of relatively small, closed environments that can be more easily modelled and validated. Such work lays foundations for the analysis of larger scale transport systems by creating a classification of the different systems and seeks to demonstrate that bike-shares have a lot to offer both as an effective method of transport and a rich source of data.
    Journal of Transport Geography 01/2014; 34:262–273.
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    ABSTRACT: We test the recently introduced radiation model against the gravity model for the system composed of England and Wales, both for commuting patterns and for public transportation flows. The analysis is performed both at macroscopic scales, i.e., at the national scale, and at microscopic scales, i.e., at the city level. It is shown that the thermodynamic limit assumption for the original radiation model significantly underestimates the commuting flows for large cities. We then generalize the radiation model, introducing the correct normalization factor for finite systems. We show that even if the gravity model has a better overall performance the parameter-free radiation model gives competitive results, especially for large scales.
    Physical Review E 08/2013; 88(2):022812.
  • Science 06/2013; 340(6139):1418-1419.
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    ABSTRACT: We investigate the growth dynamics of Greater London defined by the administrative boundary of the Greater London Authority, based on the evolution of its street network during the last two centuries. This is done by employing a unique dataset, consisting of the planar graph representation of nine time slices of Greater London's road network spanning 224 years, from 1786 to 2010. Within this time-frame, we address the concept of the metropolitan area or city in physical terms, in that urban evolution reveals observable transitions in the distribution of relevant geometrical properties. Given that London has a hard boundary enforced by its long standing green belt, we show that its street network dynamics can be described as a fractal space-filling phenomena up to a capacitated limit, whence its growth can be predicted with a striking level of accuracy. This observation is confirmed by the analytical calculation of key topological properties of the planar graph, such as the topological growth of the network and its average connectivity. This study thus represents an example of a strong violation of Gibrat's law. In particular, we are able to show analytically how London evolves from a more loop-like structure, typical of planned cities, toward a more tree-like structure, typical of self-organized cities. These observations are relevant to the discourse on sustainable urban planning with respect to the control of urban sprawl in many large cities which have developed under the conditions of spatial constraints imposed by green belts and hard urban boundaries.
    PLoS ONE 01/2013; 8(8):e69469.
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    ABSTRACT: Bicycle sharing systems exist in hundreds of cities around the world, with the aim of providing a form of public transport with the associated health and environmental benefits of cycling without the burden of private ownership and maintenance. Five cities have provided research data on the journeys (start and end time and location) taking place in their bicycle sharing system. In this paper, we employ visualization, descriptive statistics and spatial and network analysis tools to explore system usage in these cities, using techniques to investigate features specific to the unique geographies of each, and uncovering similarities between different systems. Journey displacement analysis demonstrates similar journey distances across the cities sampled, and the (out)strength rank curve for the top 50 stands in each city displays a similar scaling law for each. Community detection in the derived network can identify local pockets of use, and spatial network corrections provide the opportunity for insight above and beyond proximity/popularity correlations predicted by simple spatial interaction models.
    PLoS ONE 01/2013; 8(9):e74685.
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    ABSTRACT: Crowds are a feature of large cities, occurring not only at mass gatherings but also at routine events such as the journey to work. To address extreme crowding, various computer models for crowd movement have been developed in the past decade, and we review these and show how they can be used to identify health and safety issues. State-of-the-art models that simulate the spread of epidemics operate on a population level, but the collection of fine-scale data might enable the development of models for epidemics that operate on a microscopic scale, similar to models for crowd movement. We provide an example of such simulations, showing how an individual-based crowd model can mirror aggregate susceptible-infected-recovered models that have been the main models for epidemics so far.
    The Lancet Infectious Diseases 02/2012; 12(2):150-6.
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    ABSTRACT: A key area in the analysis of urban structural evolution is identifying discontinuities. Effective analysis could improve long-term forecasting and provide a better understanding of how to steer an urban system toward a desirable future state. We use a simple aggregate retail model to demonstrate an algorithm for identifying discontinuities in model parameter space. Explorations of retailing in both Greater London and South Yorkshire in the United Kingdom illustrate how understanding a system's potential for discontinuity can provide insights for both policy makers and retail businesses. The Harris and Wilson model, described in the section so-named, is used as a simple archetype to illustrate the new framework. This model can be developed in a straightforward way to incorporate further refinement. In “Executing the model and visualizing the results,” we describe a single model run and in “Investigating discontinuities,” we explain our framework for detecting and analyzing discontinuities. “Identifying discontinuities in the London retail system” shows the results of applying this methodology to the Greater London retail system, and in “Practical applications,” we explore the policy applications for this technique as related to the decline of town centers in the South Yorkshire retail system. Some concluding comments are offered in “Conclusions.”Un área clave en el análisis de la evolución de la estructura urbana es la identificación de discontinuidades. El uso de métodos de análisis efectivos podría mejorar los pronósticos de a largo plazo y proporcionar una mejor comprensión de cómo dirigir un sistema urbano hacia un futuro deseable. Los autores utilizan un modelo simple de venta al público agregado para demostrar la utilidad de un algoritmo que identifica discontinuidades. El conocimiento del potencial de discontinuidades en un sistema puede iluminar la acción de tomadores de decisiones de políticas urbanas y de negocios de venta. El presente artículo demuestra dicho potencial mediante el estudio de caso del comercio de venta al público en Londres y Yorkshire en el sur en el Reino Unido. Los autores utilizan el modelo de Harris y Wilson (descrito en la sección con el mismo nombre), como arquetipo para ilustrar el nuevo marco metodológico que proponen. El modelo es formulado de manera sencilla con el fin de permitir su refinamiento futuro. En la sección denominada “Ejecución del modelo y visualización de los resultados” (“Excecuting the model and visualizing the results”), se describe una ejecución del modelo. En “investigación de discontinuidades” (“investigating disconuities”) se explica el marco metodológico para la detección y análisis de las discontinuidades. La sección “Identificación de discontinuidades en el sistema de ventas al público de Londres” (“Identifying dicontinuities in the London retail system”) se muestran los resultados de la aplicación de esta metodología al sistema de ventas al público de Londres. En “aplicaciones prácticas” (“Practical applications”) se exploran las aplicaciones de esta técnica en políticas vinculadas a la decadencia de centros urbanos en el sistema de venta al público de South Yorkshire. Para finalizar, en la sección “Conclusiones” (“Conclusions”), los autores ofrecen algunas observaciones finales.
    Geographical Analysis 04/2011; 43(2):172 - 187.
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    ABSTRACT: This article details the development of a new area classification for Britain based on internal migration variables taken from the 2001 Census. An explanation of why general-purpose area classifications already in existence are not ideal for internal migration analysis is provided, before an account of the construction of the new classification is given. The latter involves justification of the choice of variables, explanation of the methodology adopted and presentation of the final typology.
    Population trends 01/2011;
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    ABSTRACT: Entropy in Urban and Regional Modelling introduced a new framework for constructing spatial interaction and associated location models. These ideas are reviewed briefly and then set in the wider context of the application of entropy in a range of disciplines. Related developments since 1970 are examined with particular reference to extensions of the core model, links to mathematical programming, the relationship to economics, and the introduction of a dynamic spatial structure hypothesis. The role of entropy maximizing in geography, and more widely in complexity science, is reviewed and two conclusions are drawn beyond the continued effective deployment of entropy models: geography could be a leading player as complexity science develops; and geography can use these ideas to update the presentation of its classic theories. The ongoing research agenda is extensive—particularly in relation to the modeling of imperfect markets in economics—in its links with network science and agent-based modeling. Recent developments in physics suggest a new role for entropy in understanding spatial structure. This article is organized into five main sections. The first summarizes the ideas of the book; the second sets this discussion in a wider context; the third surveys the developments that have taken place since its publication. The fourth summarizes the role of entropy maximizing in geography in the context of complexity science, and the fifth presents an ongoing research agenda.En el modelado urbano y regional, el concepto de entropía abre las puertas a un nuevo marco conceptual para construir modelos de interacción espacial y otros modelos de localización similares. El artículo presente reseña brevemente estas ideas y las enmarca en el contexto de la aplicación del concepto de entropía en otras disciplinas académicas. Asimismo, el autor examina el desarrollo de estas ideas desde 1970 con énfasis particular en las ampliaciones y modificaciones al modelo base original, a los vínculos con la programación matemática, en la relación con la Economía, y en la presentación de una hipótesis de la estructura espacial dinámica. El papel de la maximización de entropía en Geografía, y en general en las ciencias de la complejidad son reseñadas y dos conclusiones que van mas allá de la aplicación de los modelos de entropía son extraídas: la Geografía puede jugar un papel líder en el desarrollo de las ciencias de la complejidad; y, la Geografía puede utilizar estas ideas para actualizar la presentación de sus teorías clásicas. La agenda de investigación en curso es muy ambiciosa, en particular en relación al modelado de mercados imperfectos en Economía -en lo que respecta a sus vínculos con ciencias de redes y los modelos basados en agentes. Los avances más recientes en Física sugieren un nuevo rol del concepto de entropía para entender estructuras espaciales. El estudio presente está organizado en cinco secciones principales. La primera resume las ideas del libro (de Wilson); la segunda enmarca esta discusión en un contexto más amplio; la tercera examina los avances y el desarrollo de ideas ocurridos desde dicha publicación; la cuarta, resume el rol de la maximización de entropía en Geografía en un contexto de las ciencias de la Complejidad; y finalmente la quinta, presenta la agenda de investigación que esta en curso en la actualidad.
    Geographical Analysis 10/2010; 42(4):364 - 394.
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    ABSTRACT: Entropy measures were first introduced into geographical analysis during a period when the concept of human systems in equilibrium was in its ascendancy. In particular, entropy maximizing, in direct analogy with equilibrium statistical mechanics, provides a powerful framework in which to generate location and interaction models. This was introduced and popularized by Wilson, and it led to many different extensions that elaborate the framework rather than extend it to different kinds of models. I review two such extensions here: how space can be introduced into the formulation through defining a “spatial entropy” and how entropy can be decomposed and nested to capture spatial variation at different scales. Two obvious directions to this research remain implicit. First, the more substantive interpretations of the concept of entropy for different shapes and sizes of geographical systems have hardly been developed. Second, an explicit dynamics associated with generating probability distributions has not been attempted until quite recently with respect to the search for how power laws emerge as signatures of universality in complex systems. In short, the connections between entropy maximizing, substantive interpretations of entropy measures, and the longer-term dynamics of how equilibrium distributions are reached and maintained have not been well developed. This literature gap has many implications for future research, and, in conclusion, I sketch the need for new and different entropy measures that enable us to see how equilibrium spatial distributions can be generated as the outcomes of dynamic processes that converge to a steady state.Las medidas de entropía fueron dadas a conocer en el análisis geográfico durante un periodo en el cual el concepto de sistemas humanos en equilibrio estaba en ascenso. La maximización de entropía, de manera análoga a la mecánica estadística del equilibrio (human systems in equilibrium), proporciona un marco de gran alcance para generar modelos de localización e interacción. Estas ideas, que fueron popularizadas por Wilson (1970), precipitaron muchas ampliaciones posteriores. Estas modificaciones sin embargo, se desarrollaron dentro del mismo marco conceptual en vez de extenderse hacia otros tipos de modelos. En este artículo, el autor examina dos tipos de ampliaciones que corresponden a dos preguntas: primero, ¿cómo el espacio puede ser insertado en la formulación del modelo a través de la definición de una ‘entropía espacial’?; y segundo, ¿cómo la entropía puede ser descompuesta y anidada para capturar la variación espacial en diferentes escalas? Este tipo de investigación nos señala implícitamente dos direcciones. En primer lugar, la interpretación más sustantiva del concepto de entropía, relacionada a las formas y diferentes tamaños de los sistemas geográficos ha sido muy poco desarrollada. En segundo lugar, no es sino hasta hace muy poco que se han intentado desarrollar dinámicas explicitas asociadas a la generación de distribuciones de probabilidad ligadas a la exploración de las formas en las que leyes de potencia emergen como marcas o firmas distintivas de universalidad en sistemas complejos. En resumen, no se han desarrollado bien aun las conexiones entre la maximización de entropía, las interpretaciones sustantivas de medidas de entropía, y las dinámicas a largo plazo de las maneras en que se alcanzan y mantienen las distribuciones de equilibrio. Este vacío en la literatura tiene varias implicancias para investigaciones en el futuro. El autor concluye el estudio esbozando la necesidad de elaborar medidas de entropía nuevas y diferentes que permitan ver como las distribuciones espaciales de equilibrio pueden ser generadas como parte de los resultados de procesos dinámicos que convergen hacia estados estacionarios.
    Geographical Analysis 09/2010; 42(4):395 - 421.
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