How to find bounding boxes for Geocode radius Searches - search

Question

If I want to find all restaurants within a zip code, I can do a string search on the address, if I want to find all restaurants with 10 miles of a zip code, I need to do a location search. I have a database full of addresses and Geocodes should be no problem. But how do I compute the bounding box of an irregular shaped area, like a zip code, or city, or state or Metro Area?
Is there a tool around that does this? is this information for sale somewhere?
My initial solution is to create an estimate of the areas by searching for all addresses within them and deriving the simplest polygon that surrounds them and using that as a bounding box. However this seems a really brute force way to do this. Do I do this calculation for every city, state, and zip in my database and store it? How have other people solved this problem?

Answer 1

Companies such as Maponics have polygon data on neighborhoods, counties, cities, states, provinces, townships, etc. There may be other providers.
Many of these polygons have huge numbers of points, so you should either:
compute bounding boxes, or
precompute the zip, neighborhood, city, etc. identifier for each address, and index a search collection by these regions.
But why build your application by storing a database of places and computing geographic data on your own? You can partner with providers such as CityGrid; they provide APIs for places that can be searched by neighborhood, zip, etc.; you can use their data for free in your own local application.

Answer 2

If you happen to be using PostgreSQL for your database, you can use box(geometry) or a variation thereof to compute the bounding box for a geometry. You can also implicitly use the bounding box for a geometry in your SQL. For example (from Using PostGIS: Data Management and Queries):
SELECT road_id, road_name FROM roads WHERE roads_geom && ST_GeomFromText('POLYGON((...))',-1);
where && "tells whether the bounding box of one geometry intersects the bounding box of another".
To get the bounding box for a collection of geometries, you can first use Collect or Union to aggregate or combine all the geometries together.
Of course, if you are not using PostGIS, the functionality really comes from GEOS, which is the underlying library that PostGIS actually uses. The basic geometry functions can be used directly (from python for example) to do what you want.