I also have a cabinet full of USGS Topo Maps! There's an old teacher's story about elevation: A middle school science teacher was teaching his kids about a barometer and how it can be used to determine elevation. The teacher gave the students the assignment to find out the height of the school building. The next day, the teacher asked who had the answer? Johnny raised his hand and said "42 feet 6 inches" - which was correct. The teacher asked how did he get such an accurate number using the barometer. Johnny said " I went to the building superintendent and said if you tell me the height of the building I will give your this barometer!
I would usually bring a crow with me and put some corn on the ground at the start point, then release it from the finish. By timing how long it took to cover the distance and some simple math I could calculate the distance as the crow flies
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