The territory overlay is part of Overthrow's map rework and is not in v1.4.
Open the map and the ground the occupying faction still holds is shaded in that faction's colour. Ground the resistance has taken is left blank, so the shading answers one question: how much of the island is still occupied. It recedes as a campaign goes on, and a fully liberated island draws none of it at all.
The shading only shows control that already exists. It does not change income, stability, spawns, patrols or anything else. Capturing a place is what changes the map, never the other way round.
Four kinds of place shape the regions:
Each one pulls the ground around it towards whoever holds it, and the bigger the place the further it pulls. A base reaches further than a town, and a capital reaches further than a village. Places the resistance holds pull as well even though they are never shaded, which is why a FOB deployed inside occupied ground blanks out a patch of it, and why a captured radio tower leaves a hole in the occupier's colour.
Territory stops at the coast. Rivers and inland lakes do not divide it, so a region that spans a river is one region and that is correct.
Solid colour. The occupying faction holds this ground.
Diagonal hatching. The ground is contested: the occupier still holds it, but half or more of that town's population backs the resistance. It is the same support figure the town's own info panel shows when you click it, so the two can never disagree. Only towns can read as contested, because bases, radio towers and FOBs have no population to measure. See Town Support for what moves that number.
Blank. Nothing is drawn: either the resistance holds the ground, or it is sea.
A band along an edge. The frontier between occupied ground and ground the resistance holds. Coastlines carry no band, so a band is always a front line rather than a shoreline.
The overlay re-reads who holds what every few seconds, so a town or a base changing hands appears without closing and reopening the map. Joining a server that is already running works the same way: the shading fills in shortly after the map opens rather than waiting for the next time you open it.
The circles marking where a Mobile FOB cannot be deployed are a separate overlay drawn on top of the territory shading. Each one is drawn in the colour of the faction holding the base or radio tower at its centre, so a circle reads as the same ground rendered denser rather than as a colour of its own.
While a QRF is active, its circles are hatched as well, at a different scale from contested territory so the two do not read as the same thing.
The territory shading has its own row in the map's filter panel, as do the restricted area circles and every category of marker. See Map Filters.