How should I create a GQL query that returns the nearest entities (from my current location) based on their GeoPt property? Should I just created a 'distance' function that calculates for a set of entities with a reasonably close distance?
Thanks ahead of time!
You could store the locations in App Engine in a Quadtree structure.
Here's one description of how it would be done: Geographic Queries on Google App Engine
App Engine doesn't treat GeoPt properties specially - it has no built in spatial indexing. There are a number of third-party libraries that add support for spatial indexing, however. The best one (in my opinion) being geomodel.
geohash set very close points in different hashes so another or next layer should be preferred. you can make a radius, quadratic inside/outside shape test or even any mathematical shape and test whether the point is within our outside the shape.