The database of 1681 working maps available here was taken from the linguistic atlas ALF ("Atlas linguistique de la France"), published between 1902 and 1910 by Jules Gilliéron and Edmond Edmont in 10 volumes. About 40% of the 1421 total maps of the ALF were used to produce the 1681 working maps.
In terms of linguistic categories, 1117 of the 1681 working maps belong to phonetics (477 to vocalism and 479 to consonantism) and 471 to lexicon (vocabulary).