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Delineating the French Urban Areas Ongoing Thoughts Delineating the French urban areas Ongoing thoughts Vincent Loonis, Vianney Costemalle Geographical repositories and methods division French national institute of statistics and economic studies (Insee) EFGS, Manchester, 11th October 2019 Vincent Loonis, Vianney Costemalle Delineating the French urban areas Introduction France has delineated its urban areas at a regular pace for the past 200 years. The current definition has remained unchanged since 1962. For the next delineation, to be published in 2020, Insee has to face new challenges. Easy-to-access geospatial information leads to: scholars and official bodies questioning Insee’s implementation of the definition. increasing the number of urban area definitions (based o, population densities or built-up areas). A solution may consist in studying the robustness of the various definitions, while finding a way to combine them. Vincent Loonis, Vianney Costemalle Delineating the French urban areas Introduction Territorial classifications are classifications. As such, they are subject to statistical conventions. Some of these conventions are: classical: thresholds on population, on density rates... specific to spatial information: distance, reference system, choice of geographical layers, quality of the latter. The question raised by Insee is how to measure the influence of geographical conventions on territorial classifications. We will illustrate our ongoing thoughts with two examples: a density-based definition a built-up-area-based definition Vincent Loonis, Vianney Costemalle Delineating the French urban areas density-based definition Figure: Urban center: a cluster of contiguous 1 km2 grid cells (excluding diagonals) with a population of at least 1 500 inhabitants and a minimum global population of 50 000 inhabitants after gap-filling. (b) Urban center in Caen: 125 000 inhabitants and 3 municipalities (a) The LAEA grid Vincent Loonis, Vianney Costemalle Delineating the French urban areas density-based definition (b) leads to another delineation of (a) Another grid, with the same Caen’s urban centre, i.e. 156 000 properties as the former, inhabitants and 10 municipalities. constructed by rotation and translation, Vincent Loonis, Vianney Costemalle Delineating the French urban areas density-based definition Depending on the rotation or the translation of the grid: 17.5 million of inhabitants 431 municipalities are are always in an urban always in a so-called city centre 545 municipalities are 8.3 million are sometimes sometimes in and in and sometimes out sometimes out An average of 22.5 million An average of 684 inhabitants are classified as municipalities are classified living in an urban centre. as City. The results are robust at the national level but may be more unstable at the local level. How to manage the sensitivity while preserving the spirit of the method ? Vincent Loonis, Vianney Costemalle Delineating the French urban areas density-based definition: managing the sensitivity Consider the dwellings living in all the urban centres defined by the various rotations or translations of the official LAEA grid. Vincent Loonis, Vianney Costemalle Delineating the French urban areas density-based definition: managing the sensitivity Gather them by a 200-meter rule, you will get a delineation that is robust to the underlying choice of the grid and that fits with the French built-area-based definition. Vincent Loonis, Vianney Costemalle Delineating the French urban areas Built-up area based typologies 1 Urban units (Insee) 2 Localities (European regulation for census) 3 Sustainable development goals (UN HABITAT, indicator 11.7.1) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Urban units in France 1) continuity of build-up areas (200m between buildings) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Urban units in France 1) continuity of build-up areas (200m between buildings) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Urban units in France 2) urban area : at least 2000 inhabitants Vincent Loonis, Vianney Costemalle Delineating the French urban areas Urban units in France 3) classification on administrative units : at least 50% of population within a continuous urban area Vincent Loonis, Vianney Costemalle Delineating the French urban areas Sensitivity Classifications reduce world complexity. Some units are at the edge between two classes. these can leads to debates and disagreements We try to detect the sensitive cases of urban units classification in relation to the distance threshold. Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 1 : corridor effect Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 1 : corridor effect Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 1 : corridor effect Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 1 : inside buffer of - 100m Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 2 : very closed urban areas Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 3 : the city of Rennes Vincent Loonis, Vianney Costemalle Delineating the French urban areas Examples of sensitive units Figure: Example 3 : the city of Rennes Vincent Loonis, Vianney Costemalle Delineating the French urban areas Sensitivity typology for urban units Figure: Urban units in France according to some typology of robustness Vincent Loonis, Vianney Costemalle Delineating the French urban areas Comparison of the two approaches density based typologies / built-up area based typologies Figure: City of Chamberry Vincent Loonis, Vianney Costemalle Delineating the French urban areas Thank you for you attention ! Vincent Loonis, Vianney Costemalle Delineating the French urban areas Annex : UN HABITAT methodology Satellite imagery (city of Reims) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Annex : UN HABITAT methodology Land cover classification (made by CESBIO lab) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Annex : UN HABITAT methodology Built-up pixels coloured according to the proportion of built-up pixels within a 500m radius Vincent Loonis, Vianney Costemalle Delineating the French urban areas Annex : UN HABITAT methodology City delineation (= contiguous built-up pixels with at least 25% of built-up pixels in the neighbourhood) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Annex : UN HABITAT methodology Compared to the urban unit of Reims. Vincent Loonis, Vianney Costemalle Delineating the French urban areas Annex : UN HABITAT methodology Sometimes the match is not so good (city of Rennes) Vincent Loonis, Vianney Costemalle Delineating the French urban areas Threshold sensitivity Vincent Loonis, Vianney Costemalle Delineating the French urban areas.
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