Yes, the map maker will need several reference maps. The popular battles are easier because typically, several great historic reference maps are available. Hotchkiss produced some excellent, detailed maps. But they were not very accurate as far as scale. On the other hand, Michler produced some maps they may not have been as detailed, but the scale accuracy is stunning.. I remember lining up a Michler map to the actual digital terrain of Fredericksburg, and my jaw dropped... The scale was so close that he must have had an alien craft or something to fly over and survey the terrain.. :laugh:
I imagine that a lot of reference material is needed? After writing my post above I started wondering at the level of knowledge one would need to make a map. Specifically something like the heights you mentioned. So, I started with the Battle of Belmont as that was relatively simple and not too large and started looking at maps of it and realised that most of the ones I could find were rather useless when it comes to details and heights. So, it's a combination of various resources you need I suppose?
So thats why you need multiple maps.. And that's just for the roads, streams, wood lines, fields.. etc. The actual height data is a whole different animal. There is a method of obtaining the elevations from digital height data (or DEMs), or actually tracing a topographic map, hand coloring the contour lines.
