Yes, MAPPED is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, P 3, P 3, E 1, D 2.

Is it a valid word?

MAPPED is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

make a map of; show or establish the features of details of
explore or survey for the purpose of making a map
locate within a specific region of a chromosome in relation to known DNA or gene sequences
plan, delineate, or arrange in detail
depict as if on a map
to establish a mapping (of mathematical elements or sets)

Also: map out.