Simple, by no means exhaustive, but includes every default base in the game (airbases, airstrips, and army bases) and the one named town that exists on Sand Island.
Fun fact: 'Sand Island' is actually just the real-life Okinawan Ishigaki Island upside down, with army bases and additional airstrips, and added elevation.

This map does not include roads, land paths, accurate coloring, all of the proper details, or 50 thousand other things, mostly because this was a sidetrack of what i was actually doing, figuring out a way to 'place' items via coordinates without using the imprecise Photo Mode.

If you have any questions, feel free to ask in the comments, or contact me on Discord at @nuclearstonk
I hope this guide helps those who frequently get lost around the (admittedly small) island!