Short names for lat/long points

I want short names to refer to a specific latitude/longitude. Mostly so I can type them easily into an aviation GPS. For my purposes I need accuracy of about 1 mile, so 1 minute or .01 degree. I only need coordinates valid in the continental US, bounded roughly by 20, -125 to 50, -65. Some options, with the encoding for San Francisco (roughly at 37.75, -122.34).

  • 377512243. Lat/long base 10. 9 characters per location, and dead-ass easy to understand.
  • 9q8yvv. Geohash, a hierarchical base 32 encoding. 6 characters per location. See here for visualization.
  • KO46D. “Grid Fixes” from FltPlan. 5 characters per location. Can’t find documentation but it seems to have a resolution of 10 minutes latitude, 1 degree longitude. Not really accurate enough.
  • CM87SR. 6 characters per location. Grid Squares, aka Maidenhead Locator System, a ham radio thing, here’s a map view. Accurate to 2.5′ latitude and 5′ longitude, or roughly 4 miles, so not good enough for my purposes. There is an 8 character extended locator option.
  • ?????. Perfect rectangular coding, base 32. 5 characters per location. Need (50-20)*60 = 1800 = 11 bits of latitude, and (125-65)*60 = 3600 = 12 bits of longitude. 23 bits can be encoded in 5 characters in a base 32 representation. A base 52 representation would get it down to 4 characters.

I think if I were actually building this I’d probably go for Geohash. It has a nice property that you can specify arbitrary precision, then lop characters off the right to make a shorter code that’s less specific.