Question

I currently have a database query that calculate the distance between every store in the database from there to a “home” location. I’m calculating the flight distance using this formula.

http://www.movable-type.co.uk/scripts/latlong.html

Then I’m ordering them and displaying them. I discovered a much better way to do it is only search for stores whose latitude/longitude are within a range.

For example instead of calculating distance between each store in the database (over 30000), only group ones with lat/longs within a certain range and calculate distance between those.

Right now I’m trying to found out how to calculate the actual bounds. The distance has to be below 5km. So I divide 5 by 100 and cap the latitude and longitude by those amounts.

SELECT storeid, storedescription, address, city, storebannerdescription, lat, lon,
        ROUND (gc_dist (lat, lon, 43.758152, -79.746639), 1) AS distance
        FROM storelatlon
        WHERE ((lat-43.758152) < 0.05 AND (lat -43.758152) > -0.05) AND ( (lon-(-79.746639)) < 0.05 AND (lon-(-79.746639)) > -0.05)
        ORDER BY Distance

Answer 1

This method could work, but depending on how widely distributed your stores are, you may need to refine your bounds a bit because as you go up in latitute, you cross more longitude over a given distance. You may get too many or too few points just filtering by 0.05 deg for all latitudes.