Number of Communes in France

Interesting chart that perfectly highligths the major recent changes in French law concerning the mapping of French territory and rationalization of communes:

-1971 law of "fusions et regroupements de communes" ;

-2010 law of creation of "communes nouvelles".

Concerning the major drop in 1800-1850, this should be somehow related to Napoleonic cadastre but I can't tell more. If you have datas and files about it, I would appreciate to read them!