I'm working on a geolocation based personal project where I'd like to fetch the suppliers based on the user's latitude & longitude value. And the deal is suppliers have variable supply radius, few suppliers supply only within 5km of their radius while some may supply across the entire city.
The general way to go about this is for each supplier calculate the distance between the supplier & the user. If it is less than or equal to it's supply radius then display that supplier in the results.
But this might be very slow, so I thought I'd split the city into four zones(pick four latitude & longitude values from google maps for North East West South) & whenever a supplier is added I'll do the math & assign the zones to which they can supply in the database. Now whenever I get the user's latitude & longitude I'd determine the zone & fetch suppliers that can supply to that zone, do the distance calculation & filter them out. This way I do the calculation on less number of suppliers instead of the entire list.
But is it a good idea or can I do better ?
In you are using Postgres/Postgis, you can make use of spatial indexes, and then use ST_DWithin(geom1, geom2, distance) type queries see ST_DWithin docs. The spatial index will partition the space for you, making this kind of query very efficient and avoid you having to come up with any spatial partitioning scheme of your own.
Another operator you can use is the <-> operator, which is very efficient with a spatial index and is used in the order by clause, to get the nearest y things to some point x, (k nearest neighbour search) see <-> operator docs. One caveat for this operator to work properly with the index, the point you are searching for, needs to be a constant, as it sounds like it would be in your case.