This is a map of Paris in which the darker colors represent the higher built-up areas in buildings, according to Paris open data. This is not a building density map (you can have a big building surrounded by a large park, so density would be reduced), but rather, following what was in the last “biblio” about climate change in Paris, a map of big energy bills. So during the next days this will be the issue: big buildings, which in turn mean big energy and ressources consumers under a single management, which means (perharps) chances to go greener.