Association of State Boards of Geology ASBOG 1 Practice Exam

Isopach maps contour thickness of a bed or stratigraphic unit. They plot lines that connect points of equal thickness, revealing how the bed’s thickness varies across the area. This is different from maps that show surface elevation or topography, which contour the height of the land surface, or from maps that depict dip direction, which are based on the orientation of the bed plane. To build an isopach, thickness data are collected from wells, measured sections, or cross sections and then interpolated to create continuous contours of constant thickness. This helps visualize where a unit is thicker or thinner and can inform interpretations of deposition, erosion, and reservoir potential.