Usage patterns
〈島〉に住むto live on an island
He lives on a small island.
シマを荒らすto encroach on someone's turf
If you encroach on another gang's turf, it leads to trouble.
〈島〉を渡るto cross over to an island / travel between islands
We went sightseeing, crossing between islands by boat.
シマを守るto protect one's turf
The gang members moved to protect their turf.
Expressions
取り付く島がないleft utterly helpless; have no one to turn to; unapproachable 取り付く島もないleft utterly helpless; have no one to turn to; unapproachable