regio
Any large area of a planet or moon that is strongly differentiated from neighbouring areas by colour or albedo.
A district of a city.
The British School has unearthed a city of continuous houses, more than 400 feet long by 350 broad, whose many blocks or "insul[ae]" might seem almost to need the more elaborate grouping of the "regiones" of Pompeii.
Where it comes from
Learned borrowing from Latin regiō. Doublet of region.
Adapted from the Wiktionary entry regio (CC BY-SA 4.0).