Using Maps
There are many kinds of maps. Some can be used to find the coordinates of a location, some can find a rough coordinate, and some are just not suited for that. Many highway and street maps are marginally useful for this. Topographic maps are designed to find coordinates.
All maps are on datums, as discussed in that section. If you use GPS and a map together you should be sure the two are on the same datum.
There are other factors. All maps have distortions. They are after all, an attempt to represent a curved earth on a flat piece of paper.
If the area is large, the distortion will be large. If the area covered is small it can be much smaller.
There are two basic steps in taking a model of the curved earth and making a flat map, scaling the world and projecting it on a flat surface. They can be performed in either order. It is the flattening process that produces distortion. Map makers use some tricks to minimize this.
A final caveat. Sometimes map makers have too much information to put on a map and it would become illegble. In this case they have to make a choice. They may have to move a railroad and or a river where the two run side by side. Or the purpose of the map may dictate some feature be greatly enlarged. This is the case with highway maps. This is called cartographic license.
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