Geocoding: Entertaining results

Recently I was working on a project which had a need for geocoding. Normally we use PostGIS along with some free data for geocoding. However, to cross check data and to verify results I decided to write a little Python function to see what Google would actually give me.

To come up with the Python function the first thing to do is to install geopy, a module freely available on the web:

root@chantal:/tmp# git clone https://github.com/geopy/geopy
Cloning into 'geopy'...
remote: Counting objects: 2848, done.
remote: Total 2848 (delta 0), reused 0 (delta 0)
Receiving objects: 100% (2848/2848), 913.77 KiB | 504 KiB/s, done.
Resolving deltas: 100% (1841/1841), done.

The stuff can be compiled and deployed easily:

root@chantal:/tmp# cd geopy/
root@chantal:/tmp/geopy# python setup.py install

Then PL/Python has to be enabled:

test=# CREATE LANGUAGE plpythonu;
CREATE LANGUAGE

Then the function can already be written. The first thing I have done here is to come up with a data type returned by the function. In the example the position, the longitude and the latitude are relevant:

CREATE TYPE v_position AS
(
        location            text,
        lat                 numeric,
        lng                 numeric
);

Finally there is the function itself, which connects to Google and fetches some data. It is more or less trivial:

CREATE OR REPLACE FUNCTION geo (raw_string text)
        returns setof v_position AS
$$
from geopy import geocoders
geocoder = geocoders.GoogleV3()

try:
        for res in geocoder.geocode(raw_string, exactly_one=False):
                yield {'location': res[0], 'lat': res[1][0], 'lng': res[1][1]}
except:
        pass

$$ LANGUAGE plpythonu VOLATILE;

Now we can test the function with some sane input:

test=# \x
Expanded display is on.
test=# SELECT * FROM geo('groehrmuehlgasse 26, wiener neustadt');
-[ RECORD 1 ]----------------------------------------------
location | Gröhrmühlgasse 26, 2700 Wiener Neustadt, Austria
lat      | 47.8178812
lng      | 16.2384326

The result gives us the position of our Cybertec headquarter here in Austria. So far so good …

Unexpected results …

To see if my function works properly I tried to come up with a string, which seemed pretty unlikely to me:

test=# SELECT * FROM geo('dirt hole');
-[ RECORD 1 ]--------------------------------------------------
location | Dirt Hole Creek Road, Tambaroora NSW 2795, Australia
lat      | -32.9826131
lng      | 149.4264436

Well, obviously some places are not blessed with proper names. There seem to be dirt holes in Australia after all 😉

Let us focus our attention on some more “religious” question:

test=# SELECT * FROM geo('infidel');
-[ RECORD 1 ]-----------------------------------------------
location | Infidel Place, Torbay, Auckland 0630, New Zealand
lat      | -36.7024209
lng      | 174.746813

It seems that even this leads to a result …

But, this is pointless.

test=# SELECT * FROM geo('pointless');
-[ RECORD 1 ]--------------------------------------------
location | Truax SE5, Squamish-Lillooet A, BC V0N, Canada
lat      | 50.7844444
lng      | -122.6816666

… or maybe just insane …

test=# SELECT * FROM geo('insane');
-[ RECORD 1 ]--------------------------------------------------------
location | Insane, 115 21 Stockholm, Sweden
lat      | 59.3236986
lng      | 18.095511

-[ RECORD 2 ]--------------------------------------------------------
location | Insane, The Tongass National Forest, Juneau, AK 99801, USA
lat      | 58.2691792
lng      | -134.5122587

Maybe we should not trust everything returned by a webservice

We have some more great GIS posts for your right here on our GIS blog spot… enjoy!