ambit

ambit - noun - circuit or compass; the boundaries or limits of a district or place; an area in which something acts, operates or has power or control; extent; sphere; scope

Last night I was teaching SafeKids about their "circle of safety". That is the area around you over which you exert personal control. If you allow someone close enough to reach into that space, you risk capture by bad-guys. Sure wish I could have used this word, but a bunch of 5-11 year old kids just wouldn't have understood it and it would have taken as long to explain it as it did to just describe the concept.