Natural boundaries
Open/Close, type, intensity, visibility, impact to movement
Hills, valleys, mountains, etc.
Lakes, rivers, swamps, currents, direction of travel, depth
Roads, highways, rail lines, bridges/culverts, power lines, etc.
Towns, significant factories, industrial parks, etc.
Minefields, ditches, abatis, fences, etc.
Boundaries, report lines, line of departure, etc.