I'm not sure what the correct term is, but it's a common cartographic design pattern.
I want to show the outline of built-up areas as a filled polygon beneath road and buildings layers.
In OpenStreetMap, such areas are sometimes available as landuse=residential. I suspect these will all have been traced manually.
Here's an example, this is Gibraltar. I digitzed this outline manually and clipped it to the shoreline. The "urban footprint" consists of the purple/pink areas (this was extended out to sea, then clipped to the land outline from OpenStreetMapData)
Is there a tool available in QGIS (or other FOSS GIS tools) to generate these automatically from a set of buildings?
Two approaches I've tried already...
- I tried the Concave hull plugin but only got a single area.
- I also tried a Delauney Triangulation on nodes extracted from the building outlines. I suspect if I can discard large polygons or those with very acute angles between vertices, that might work...