Improve algorithm to find the N closest cities to current location about webapp HOT 1 OPEN

This may not solve it for all cases, but if you want a quick solution, you could potentially add a filter right after calculating size to only include cities within X units ( 50 miles, 100 km, whatever you want). It doesn't "in theory" reduce it to a small amount, but in practice we know a set of coordinates is only going to be close to some small set of cities.
You may end up with less than 6 so I'm not sure if that's suitable for you but just another potential solution that goes a different way entirely.

from webapp.