24 mars 2021
Claire Lagesse et al., « Reading road networks through time: How structural changes affect territorial accessibility ? », HAL-SHS : géographie, ID : 10670/1.8y8sjv
City Road networks extend through time according to territorial constraints and local policies. This work focuses on the geographical and geometrical aspects of the road network skeleton. Following on the work on space syntax and successors (Hillier 1976, Hillier 2007, Porta 2006), an extended geographical object called the way is built, by pairing edges at each node of the road network graph. The way is constructed by local geographical rules, independently from the order in which the network is read. The resulting object is multi- scale, from the single edge to the largest way extending over the whole studied zone.This last property allows to make stable computations on as large as wanted geographical zones. Topological indicators computed on the ways (as degree centrality or closeness centrality) gain the valuable property to become robust against zoning. Large scale examples (Paris, Avignon, Rotterdam) will illustrate how these indicators computed on ways are revealing city structure. In particular the stability through zoning also implies stability through time (which can be considered as a more complex zone variation). It is then possible to read the history of cities, through the lines of their road networks, including major events as the impact of piercings. From the ancient core to the newest suburbs, the dynamics of expansion is highlighted (cf figure 1).Further the analysis of the current structure, characterization of network evolution (over three centuries on Avignon ; five on Rotterdam) allows to observe the variation of accessibility on space, and thus to better understand the impact of urban planners decisions. Through the results of different indicators, it will be possible to quantify the impact of urban projects, and better understand the dynamics of evolution in cities.As road network geometry is difficult to obtain on a large scale of time, a collaborative digitalization of ancient maps' street networks appear to be a valuable solution to build a substantive database. The project Covadeo (support by Burgundy – Franche-Comté region) aim to develop a collaborative platform of crowdsourcing. A smart game will be elaborate, allowing the collectivity to contribute to a large geo-historical database of road networks expansion through time. From those data, it will become possible to analyze over several cities the development of road networks, compare them, and understand how territorial accessibility move from one polarization to another.The way, built upon appropriate parameterization, allows us to carry out deep analysis of spatial networks, independent from their size and borders. The obtained results have shown their relevance for urban planners, as they match their way of reading cities. The new indicators expand their possibility of analyses. The collaborative database aims the comparison between different territories, with different histories and dynamics. It allows to link quantitative and qualitative approaches and fosters multidisciplinary discussions.