For decades, cities have been expanding outward, taking up more and more space and in many cases merging beyond their administrative boundaries. In contrast to this trend, a different one has begun to develop: the inward growth of cities.
Urban infill seeks precisely to reverse urban sprawl and recover the traditional model of compact and sustainable cities. It does so by increasing the buildability of built-up areas, modifying the housing typology, building on empty plots or promoting mixed land uses, with the integration of main daily activities in the same space. In contrast to the sprawling neighbourhoods that force people to travel long distances to go shopping or to the cinema, and increase the use of private vehicles, urban infill promotes environmental sustainability and active mobility by bringing the services needed in our daily lives closer to the places where we live.
The evidence for Spain shows that it is in cities with higher urban density that more proximity trips are made and that residents live closer to essential services such as schools, health centres and supermarkets [Figs. 1 and 2].
Urban density: number of people per km2 of residential land. The residential area of each municipality has been obtained from Indicadores urbanos and the population from the Censo Anual de Población, both sources of the Instituto Nacional de Estadística. Proximity mobility: percentage of trips with a distance of less than 2 kilometres out of the total number of trips made in a municipality. Only trips originating from the home where the person lives are taken into account. The source is Open Data Movilidad of Ministerio de Transportes y Movilidad Sostenible. Proximity services: average percentage of dwellings in each municipality that are close to basic services such as schools, hospitals and health centres, supermarkets, pharmacies and bars, and restaurants. The source is the Encuesta de Características Esenciales de la Población y las Viviendas of Instituto Nacional de Estadística.
In the Anglo-Saxon countries, the standard-bearer of the urban sprawl model, the paradigm shift towards urban infill is gaining importance. Cities such as Toronto, Portland and Auckland, to mention just a few, have already opted for this model. In Spain, Vitoria-Gasteiz is an example with its urban infill plan for Salburua and Zabalgana, two of its largest districts.
If this model is generalised, the cities of the future could become networks of several interconnected centres capable of providing the main daily services within walking distance.
For more information, please see: Bajo, Fernando. "Otros procedimientos de intervención en la ciudad contemporánea: sobre la re-densificación." ACE: Arquitectura, Ciudad y Entorno 15, 2021; Greenaway-McGrevy, Ryan, y James Allan Jones. "Can zoning reform change urban development patterns? Evidence from Auckland." Urban Studies 0, 2025; City of Toronto. The Good Neighbour Guide. For residential infill construction; Newman, Peter, y Jeffrey Kenworthy. "Gasoline consumption and cities revisited: What have we learnt?" Current Urban Studies 9, 2021; Sony CLS. "15min-City." Sony Computer Science Laboratories Rome.