Mexican municipio code
The five-digit code identifying a Mexican municipality in the geostatistical catalog kept by INEGI.
Five digits: the two-digit state followed by three digits for the municipality within it. Abala in Yucatan is 31001; Acala in Chiapas is 07002.
The leading zero is part of the key. INEGI's own catalog documentation writes the composition out as state key plus municipal key, so 01001 read as the number 1001 points at a different municipality entirely.
The five-digit key always means a municipality and only a municipality. A locality inside one takes the nine-digit Mexican localidad code instead, and the two must not be interchanged: municipality and locality names repeat across Mexico, and several localities carry the name of a municipality in another state.