indexing nodes: quadtile vs lat/long

[anandthakker]

We should investigate whether we're benefitting from the current approach to indexing Nodes with a quadtile index. The alternative would be to index both the latitude and longitude columns in the nodes table so that we could do WHERE BETWEEN queries on lat and long.

[kamicut]

This is where the quadtile query is used in openstreetmap: https://github.com/openstreetmap/openstreetmap-website/blob/master/lib/osm.rb#L544-L551