1973, in computer jargon, from bit (n.2) + map. Literally, a map of bits.
Entries linking to bitmap
bit n.2
computerese word, 1948, coined by U.S. computer pioneer John W. Tukey, an abbreviation of binary digit, probably chosen for its identity with bit (n.1).
map n.
"drawing upon a plane surface representing a part or whole of the earth's surface or the heavens, with the various points drawn in proportion and in corresponding positions," 1520s, a shortening of Middle English mapemounde "map of the world" (late 14c.), and in part from French mappe, shortening of Old French mapemonde. Both the fuller English and French words are from Medieval Latin mappa mundi "map of the world."
The first element is from Latin mappa "napkin, cloth" (on which maps were drawn), "tablecloth, signal-cloth, flag," said by Quintilian to be of Punic (Semitic) origin (compare Talmudic Hebrew mappa, contraction of Mishnaic menaphah "a fluttering banner, streaming cloth"). The second element is Latin mundi "of the world," from mundus "universe, world" (see mundane).
Commonly used 17c. in a figurative sense of "epitome; detailed representation of anything." To put (something) on the map "bring it to wide attention" is from 1913.