This image of Baltimore shows many reservoirs: directly north of the city is Loch Raven, At the top center of the image is Pretty Boy, just northwest of the image center is Liberty with Piney Run lake just west of that, about 1/5 from the bottom and left of the center of the image is the thin sinuous Rocky Gorge, and just upstream (northwest) is Tridelphia. The last two reservoirs are part of the D.C. water supply. The horizontal wooded river valley just south of Liberty Lake and Piney Run lake is the Patapsco valley. The valley containing Rocky Gorge and Tridelphia reservoirs is the Patuxent valley. Together these outline most of Howard county, and where they nearly touch, at their western ends, is Parr's spring, a pond where 4 counties touch: Howard, Carroll, Frederick, and Montgomery. Baltimore Washington International Airport (BWI) is just visible south of Baltimore. For this image every 5th pixel of every 5th line has been displayed.