 We are often interested in finding distances on the map so that we can calculate quantities we are interested in, such as the temperature gradient. Note first that often the projection of the map that we have does not have east-west parallel and straight across. In fact, the east-west line is curved a little bit. So take that into account when you're doing your calculations. Also note that the north-south lines run a little bit, not parallel as well. Okay, so how do we find distances? Well, there are many different ways, but one good way is to take a known distance on the map, scale it with a ruler, and then use that ruler in other places to give us distances in other places. So, for instance, we know that the height of Pennsylvania between the two parallel borders, the north and south borders, is 135 nautical miles. So, we can scale that with a ruler, and I have a ruler here, so I put the ruler in, and I see in this particular case the distance between the two is just about exactly one centimeter or ten millimeters. So what that means is each millimeter on my scale is equal to 13.5 nautical miles on the map. So then I can use this in other places to measure other distances. So, for instance, if I want to know the height of Kansas between its parallel north and south borders, I can put my ruler on there, and if I look carefully, I get a number that's about 13.5 millimeters. So 13.5 times 13.5 is about 182, and that's what I would say this distance is. The actual distance is 180 nautical miles, so in fact the scaling I have is actually pretty good.