Question

Why are maps drawn from above (vertically) more accurate for measuring distance than maps drawn from the side (oblique)?

Answer 1

Techniques for depicting terrain from directly above were developed for two primary reasons. First, the oblique view inherently hides some map features; a vertical view, by contrast, offers a view of all landscape features within the map frame. The vertical view also allows the map maker to position features appropriately in geographic space—thus providing concrete spatial information, rather than a more artistic visual representation.

In the vertical view, terrain is typically represented with contour lines. Contour lines drawn on a map connect points of equivalent elevation. Figure 6.4.1 demonstrates how contour lines relate to the landscape from which they are derived—note that the bottom image is a 2D rendering of what is presumed to be a regularly-shaped mountain feature.