Whereas the satellite image was taken approximately 500 miles in outer space, this image was made by a reconnaissance flight at approximately 10,000 feet in altitude. When geographic scale has been increased, then area is reduced thus giving more detail to the landscape. The above aerial photo represents an iconic model because is shows a landscape precisely as it was when the photograph was taken. It is from iconic models that an analogue model can be created. The below map is an analogue model because cartographers have used abstract symbols to reflect actual attributes of the landscape as shown in the aerial photo.
Maps are abstractions of reality using symbols analogous to real features on Earth s surface.
The closer the contour lines to each other indicates a steep relief. The line drawn across the water gap in both aerial photo and map indicates the segment of the water gap that we want to investigate. By placing graph paper across the water gap and noting where the contour lines intersect with the graph, we can construct an exaggerated profile of the water gap. The above profile of the water gap at Point of Rocks suggests that the flow rate of the Potomac over the past two million years as being fluxional. Note the similarity between the wind gap and the river terrace.