Isopach map
![Isopach map showing true stratigraphic thickness of Holocene sediments deposited offshore of Pacifica, California](/Images/godic/202501/21/Isopach_Sheet7d_335802.jpg")
An isopach map illustrates thickness variations within a tabular unit, layer or stratum. Isopachs are contour lines of equal thickness over an area. Isopach maps are utilized in hydrographic survey, stratigraphy, sedimentology, structural geology, petroleum geology and volcanology.