Question

I have a table in postgresql 9.2 that stores the latitude and longitude of locations as integer values.

I intend to do something like when a user searches for a location, he also gets information on other locations that are within a 7 mile radius of that searched location.

How do i use postGIS for this since i am new to it. Any idea.?

Answer 1

You’ll actually want to store the latitude and longitude as a point.

CREATE TABLE postal_codes
(
  zip character varying(7) NOT NULL,
  state character(2) NOT NULL,
  city character varying(50) NOT NULL,
  geoloc geography(Point,4326) NOT NULL
);
INSERT INTO postal_codes
VALUES (
    '35004', 'AL', 'Moody',
    ST_GeographyFromText('SRID=4326;POINT(-86.50249 33.606379)') -- lon lat
);

You can then get all points within a certain distance using STDWithin.

SELECT geoloc
FROM postal_codes
WHERE ST_DWithin(
    geoloc,                            -- The current point being evaluated
    'thegeolocyoustoredawaysomewhere', -- the location of the person
                                       -- you're giving info to
    7 * 1.6 * 1000                     -- Miles to meters
);

Or:

SELECT geoloc
FROM postal_codes
WHERE ST_DWithin(
    geoloc,
    (
        SELECT geoloc
        FROM postal_codes
        WHERE zip = '12345'
    ),
    7 * 1.6 * 1000
);

To boost performance a bit for other kinds of queries (not any seen here), use a GiST index:

CREATE INDEX geoloc_idx
ON postal_codes
USING gist (geoloc);