The funny thing about depictions of ISIS' areas of operation and control on maps provided by, say... The New York Times, is that they're always shown as wispy red tendrils curling along main highways and around towns, and that level of spin is a bit silly.

The point being that there's some sort of psychological effort being made, to assert that while all the main roads are under control, and all the main roads certainly surround much larger areas, ISIS only controls the first 25 feet outside of the roadway, as if it's bound by some sort of municipal Iraqi or Syrian zoning ordinance.

ISIS doesn't have an Air Force; they can't really defend the desert they don't occupy event if it's terrorist with little strategic importance.

Had the maps shown ISIS with more territory someone might suggest a psychoigical effort was being made to scare people into supporting a more direct conflict with ISIS.

I do think it would be interesting to know how journalists draw these maps though.

I dunno. Technicalities of vertical envelopment aside, once something is surrounded it's usually considered ceded to those who have it surrounded.

An inability to defend, contrasted with an unlikely target to be attacked, leaves you with ease of access as a defining quality of possession.