Christian Heilmann

Posts Tagged ‘location’

Finding the current location by IP and with the W3C Geo API

Monday, January 25th, 2010

I was always fascinated by those ads that show you “hot contacts in {city}” not because of the hot contacts, but because they always changed to where I was at the time.

I was also quite interested in the fact that they were always a bit off (again, the city, not the contacts). As I like to find things out, here’s a demo of just how far the location of these ads can be off:

The difference between IP location and Geo location by  you.

You can see your results by visiting the demo page and allowing it to get your location if you use a browser that supports the W3C geo location API.

Here’s how this works:

You can guess the location of a user by their IP and Rasmus Lerdorf wrote a nice API to do that at Using that, you can read the IP in PHP and call the API with cURL:

} else {

$url = ‘’.$ip.’&format=json’;
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);
$data = json_decode($output);
$lat = $data->latitude;
$lon = $data->longitude;

This API is only a wrapper for the Maxmind API and for some reason rounds the latitude and longitude from time to time. You can get more accurate results using the Javascript Web Service of Maxmind directly:

The most detailed data can be obtained with the W3C Geo API though:

var lat = position.coords.latitude;
var lon = position.coords.longitude

And that is all there is to it :)

Geo this! Geolocate WordPress posts with Greasemonkey and Yahoo Placemaker

Monday, June 22nd, 2009

Geolocating content on the web is a great idea. By embedding latitude and longitude and real place names in your document you allow data mining for location or easy display on a map.

The problem up to now was that it is quite a job to find out the correct geo information from a text or a document and it is quite a pain to enter the information by hand.

Yahoo Placemaker is a web service that helps you with that – you give it some text or a document URL and it returns you all the things it found in there that resemble a geographical location back. The issue with doing that on a live site is that you slow down your site immensely as you need to look up every time.

The more logical place to do the lookup with Placemaker is when you edit your document. I thought this would be cool to have for this WordPress install here and wrote a small GreaseMonkey script that injects a new “Geo this!” button in the main WP form:

Geo this - button by  you.

When I hit the button the script does an Ajax request using the Placemaker open YQL table to get the information for the currently edited text.

Once it found the information it adds it at the end of the document as a GEO microformat. Each found entry starts with a comment that tells you what Placemaker matched and considered a geographical location. As it is not infallible this makes it easy for you to delete wrong entries.

Geo this - added microformats by  you.

Try it out yourself:

This is pretty much rough and ready and I’d be happy for feedback how to improve it.