The heartland of this region stretches across the southernmost half of the 64,000 square mile Chesapeake drainage, a vast area bounded on the north by the headwaters of the Susquehanna River in southcentral New York, on the west by the Appalachian Mountain chain crests that cut across central Pennsylvania and West Virginia, and on the south by the upper tributaries of the James and other rivers that flow into the lowermost reaches of Chesapeake Bay

The Chesapeake Bay heartland itself is bordered on the west by the Blue Ridge Mountains in Virginia and the Catoctin Mountains in Maryland and Pennsylvania. A broken line of low hills running parallel to Pennsylvania's Kittatiny Mountains forms its northernmost border, and the elevated uplands separating the Delaware and Susquehanna drainages forms its eastern border. The heartland's southern borders are in southeastern Virginia, marked by the headwaters of rivers and streams that flow north and east into the Bay's lowermost reaches.

This region contains three distinct, occasionally overlapping environmental areas often called physiographic provinces or ecosystems by specialists. These are the Bay, itself, the coastal plain, and the Piedmont. Each is a unique and complex environment that supports and is influenced by living things. The Bay environment consists of deep and shallow open salt waters and the brackish waters of the lower tidal portions of rivers. Chesapeake waters flow into the Atlantic Ocean at Hampton Roads at the Bay's southeastern end. The coastal plain bordering on the Bay consists of beaches, marshes, forests, and grasslands growing on generally sandy or gravelly soils. This area is often called the tidewater region, since the waters coursing along its shores rises and falls with the tide. Coastal plain sections on the Bay's eastern and southern shores generally tend to be flat and are drained by salty or brackish waters. Bluffs and low rolling hills drained by brackish or freshwater streams are located on the western shore and in more interior parts of this region.

The Piedmont (literally "foot hills") is a region of mixed hardwood forests and softwood barrenlands bordering on swift-running freshwater rivers and streams. Low mountain chains and isolated hills of hard rock resistant to eroding power of these waters rise above broad valleys covered by soft clayey soils. A lowlying ridge chain, known as the fall line, runs through the region from Conowingo Falls on the Susquehanna to Baltimore, Washington, and Richmond. The fall line separates the Piedmont uplands from the tidal lowlands of the coastal plain. Rapids flowing over this ridge line mark the uppermost limits of navigation for ships sailing up the region's rivers. These distances vary from less than five miles on the Susquehanna to well over 100 miles on the James.