found: Form/genre for cartographic materials [draft of LC working group], 1996:Diagrams--Block (A perspective map of a segment of the land portrayed as if removed from its adjacent areas and showing the underlying rock formations on the front and sometimes also the sides of the block. Block diagrams may also be used to illustrate subterranean structures)
found: LCSH, April 28, 2010:(hdg.: Block diagrams)
found: OED online, April 28, 2010:block (def. 23a: block diagram: a type of relief model)
notfound: Glossary of mapping, charting,and geodetic terms, 1973
