Renaming
TKMapScale
TKVisibilityContext
shouldHide to shouldShow, for cleaner interface
Correct the TKMapScale version of visibility constraint
Optimize visibility checks: only get visibility context once
TKMKMapRectFromCoordinateRegion
Calculate altitude and TKMapScale for a target coordinate region
Add willZoomMapToVisibility to allow preemptively removing map objects before zooming out