I used an ordered_set ets table inserting records like

{Latitude, Longitude, Record}

Then when looking things up given an input latitude and longitude, I would
add/subtract a small number of degrees to the input to get a range of
latitudes and longitudes.

Then query ets first using ets:prev/2 with the input latitude and walking
down by repeatedly calling ets:prev/2 until I either hit the start of the
table or the lower bound on the latitude.

You then do the same with ets:next/2 to the upper bound and
finally ets:lookup/2 in case its an exact match.

I would pass the upper and lower bound of the longitude along so I could
filter out things out of range as I was walking through the latitudes.

I've got about 60000 entries in the ets table and queries take about
0.085 milliseconds on average.  I found that using ets:prev/2 and ets:next/2
was much faster than say ets:match with a matchspec to do the range
checking.  I've also got another ordered_set table with 11 million entries
which I don't do range checks but just an ets:prev/2 and an ets:lookup/2
and that runs even faster (average about 0.010 millis per pair of calls).

Unfortunately the code is not shareable, but its relatively straightforward
so shouldn't be hard to recreate.

Good Luck,

-Anthony