The database of 3911 working maps available here was taken from the linguistic atlas AIS (Atlante Italo-Svizzero, recte: "Sprach- und Sachatlas Italiens und der Südschweiz"), published between 1928 and 1940 by Karl Jaberg and Jakob Jud in eight volumes. All 1705 original maps of the AIS were used for the production of the 3911 working maps, but with the consistent exclusion of AIS maps with too many missing data.
In terms of linguistic categories, of the 3911 working cards, 1766 belong to phonetics (873 to vocalism and 805 to consonantism) and 1225 to lexicon (vocabulary).