For example, the Kingdom of Hungary is divided into 8 sub-entities: Burgenland, Croatia, Guns, Little Ruthenia, Nyatria, Ruthenia, Upper Hungary and the West Border. Alternately, the Colony of Archangel has no sub-entities; therefore, the whole Colony is considered to be one locus.
Sub-entities will be of very different sizes; the size, or number of hexes, has no effect on the definition of a locus.
Possessing knowledge of a locus (sage ability) would mean that the character had chosen which sub-entity the character wished to know very well.
If, for example, a character with knowledge of Geography chose the locus of Croatia, then that character would have specific and detailed knowledge of the geography of that specific locus.