When I look at a USGS topo map, how high would I be flying to see the area described by that map?

Question

A USGS map for a particular quadrangle in the 7.5 minute series has a scale of 2 5/8 " equaling one mile on the map. A map, then, shows about 7 miles in width. At what altitude would I be able to see this 7 mile wide swath?

Answer 1

It depends on how far away you hold your map when you're looking at it! Or in other words, how big a proportion of your field of view the maps taking up. For the sake of ease, we'll assume you're looking at it from 20 50/8" (Or 25 1/4"). But you can fill in your own number below...

This question is easier than you think it is. What you're talking about are two triangles that are propotional to each other. So: (Ignore the dots! They're there for spacing!)

x m.. 25 1/4"
----- = --------- = 10
1 m... 2 5/8"

The height (in miles) you will have to be above the ground to look at 1 mile of real terrain in the same way that you see 2 5/8" of map from 25 1/4" height is 10. In this example.

And having gone skydiving from several miles up myself, I can tell you that a lot of the terrian pretty much DOES look like a map from that height!