1. n. [Geology]

A contour that connects points of equal thickness. Commonly, the isopachs, or contours that make up an isopach map, display the stratigraphic thickness of a rock unit as opposed to the true vertical thickness. Isopachs are true stratigraphic thicknesses; i.e., perpendicular to bedding surfaces.

See: contour,  contour interval,  contour map,  formation,  isochore,  reservoir,  stratigraphy,  true stratigraphic thickness,  true vertical thickness