Mud map

Mud map is an Australian term for an informal map, intended to assist, but with no pretentions to accuracy or completeness. The term originates in such a map drawn in mud or dust with a stick, perhaps in response to a query by a stranger.

Examples of use
"Now comes the keystone to understanding between black and white — the mud map." "Left: A New Zealand soldier provides a lesson on using mud maps during the TGT-7 mission rehearsal exercise."