This report presents a map showing the potentiometric surface of the Lower Patapsco aquifer in the Patapsco Formation of Lower Cretaceous age in Southern Maryland during September 2002. The map is based on water-level measurements in 69 wells. The highest measured water level was 108 feet above sea level near the northwestern boundary and outcrop area of the aquifer in northern Anne Arundel County. From this area, the potentiometric surface declined towards large well fields at Severndale, Arnold, and Annapolis. The measured ground-water levels declined to 87 feet below sea level at Severndale, 39 feet below sea level at Arnold, and 43 feet below sea level a few miles west of Annapolis. There was also a cone of depression covering a large area in Charles County that includes Waldorf, LaPlata, Indian Head, and the Morgantown power plant. The ground-water levels measured were as low as 191 feet below sea level at Waldorf, 131 feet below sea level at LaPlata, 115 feet below sea level at Indian Head, and 86 feet below sea level at the Morgantown power plant.