If you use 20 bytes for the city name and 6 bytes for the GPS coordinate (no need to be too precise in a case like this) you can fit 880 city names in a file th

If you use 20 bytes for the city name and 6 bytes for the GPS coordinate (no need to be too precise in a case like this) you can fit 880 city names in a file that size. The program could then search the file to see which city was closest. There are only about 300 cities in the world with more than a million residents, so use the remaining 580 slots to fill in all the gaps with sensible names, and you might have something workable. It'd especially work if you added "Area" at the end, as in "Denver, Colorado Area".