This database of 375 working maps was extracted from the linguistic atlas ALPI ("Atlas lingüístico de la Península Ibérica"), of which only a single volume exists in printed form (Madrid: CSIC 1962). Of the 75 original maps contained in this volume, only 62 could be dialectometrically evaluated for various reasons. The 375 working maps mentioned above were extracted from these.

From a categorical point of view, 331 of the 375 working maps belong to phonetics (of which 189 relate to vocalism and 142 to consonantism) and 42 to the lexicon (vocabulary).

Webpage of the ALPI: