Following the concept that a blog is life's laboratory notebook, this is as much a post to myself as it is anything else. Disregard at your leisure.
As some of you may know, the kids and I are working on a geography game. In it, you will run an import/export business. You will buy things like lumber, fish, electronics, machine tools and so on in the places where they are found and ship them to the places that import them. The most difficult thing about the game design so far has been the map.
The problem is that the Earth is dominated by vast, unpopulated areas like the Pacific Ocean and Asian Russia. Populated areas are compact. For example, I want to have both San Diego and Los Angeles in the game. They are 120 miles apart in real life. In order to make them far enough apart on the map so that you can tell which one your pawn is on, they need to be 1" apart on the map. That gives us a map scale of 120 miles to the inch.
The Earth is 24,860 miles around at the Equator. At this scale, the map will have to be 17 feet across. While that would be loads of fun to do (imagine a geography version of Twister) it is totally impractical.
That means we have to go to map inserts. It turns out that Europe, North America and Japan will require inserts. The inserts will be at 120 miles to the inch, allowing the rest of the map to be smaller.
The continental US (CONUS to you military types) is about 3000 miles across. At this scale, the North American insert will have to be 2' across. Europe would be something similar.
This leaves you with the issue of where to stick Europe and North America on the map. Of course, you could just do inserts for the dense parts of Europe and America, places where the Earth map is too small to cover it.
Working backwards, if I want an Earth map that is 4' across, then I need a scale of about 520 miles to the inch. Any cities that are closer than 520 miles apart will need an insert.
Working backwards from the game mechanics, I did some research and decided that a freighter travels at 18 knots, on average. In a 24 hour period, it can travel about 497 statute miles at sea. In order for the players to know which sea lane tick mark their freighter is on, we will need a 497 miles to the inch scale. That works out to the 4' map as well. Hmm. Looks like that's settled then. 520 miles to the inch it is.