1. n. [Geology]

A type of subsurface map whose contours represent the elevation of a particular formation, reservoir or geologic marker in space, such that folds, faults and other geologic structures are clearly displayed. Its appearance is similar to that of a topographic map, but a topographic map displays elevations of the Earth's surface and a structure map displays the elevation of a particular rock layer, generally beneath the surface.

See: contour,  contour interval,  contour map,  depth map,  formation,  structure,  topographic map