My partner Doug found this page of free map tools. They do things like highlight a circle defined by a radius, calculate area, and give distances between two points. Gee, this would've been useful when Ng_moonmoth and I were trying to do all the calculations for the Massacre of Cascabel. (Yes, we did calculations, using some historic examples and modern statistics for inspiration.) So if you're a writer, this may be stuff you can use too. Especially the radius tool, that one is good for craters, kill zones, hurricanes, earthquakes, all kinds of stuff.