An isopach map is used to show variation in what characteristic?

• A. Dip variations of beds
• B. Thickness variations of a stratigraphic unit
• C. Porosity distribution
• D. Permeability distribution

Answer: (B)

Isopach maps are used to show how thick a stratigraphic unit is across an area. They’re a contour representation where each line marks places with the same thickness, so you can see where the unit thickens or thins. This helps you interpret depositional patterns, potential pinch-outs, and variations in sediment supply or accommodation space. It’s not about the tilt of the beds (that would be shown on a dip map) or about rock properties like porosity or permeability, which describe pore spaces and fluid flow rather than geometric thickness. So the characteristic being mapped is the thickness variation of a stratigraphic unit.