Urban spot in Auvergne-Rhône-Alpes

Takeover of the urban spot in the Auvergne-Rhône-Alpes region, over several years The method is to generalise the objects of the BD Topo® database, the only large-scale vector database, following the method defined by the ex-CETE of the South West (now CEREMA) in 2008. Urban spot is defined here as urbanised areas, industrial areas or commercial and airport areas. The BD Topo® is a vector database of the IGN available since 2007 throughout the French territory. With a metric accuracy, it allows exploitation up to a scale of 1/10 000 or even 1/5 000. As the Topo® BD essentially includes simple geographical objects such as buildings or sometimes areas of activity, it is necessary to obtain an urban spot to perform a mathematical morphology operation called “urban spot closure”. This closure is the combination of two basic operations: a dilation and one, erosion. The expansion consists of aggregating buildings that are less than D meters apart. To do this, a buffer is created from each object. The buffer is a polygon encompassing the area within a radius of R=D/2 around an object. Erosion consists of giving back to the objects their initial size by leaving together the objects that have been aggregated. To do this, a negative “-R” radius buffer is applied. As part of this method and following the specifications proposed by Certu in 2005 (now CEREMA), a 50-metre closure was applied to the data thus processed.