Jef Claes

On software and life

19 Dec 2010

HTML5: The Geolocation API is scary (good)

I read about the HTML5 Geolocation API in the Pro HTML5 Programming book a while ago, and decided to play with it on this lazy Sunday.

Using the Geolocation API to make a one-shot position request is very straight-forward. Get a reference to the navigator.geolocation object and call the getCurrentPosition() method, passing in at least a PositionCallback. In this example I’m also passing in a PositionErrorCallback. In the PositionCallback you can examine the properties of the position object. Here I am only using the latitude and longitude properties.

function showLocation() {                       
    if (navigator.geolocation) {
        navigator.geolocation.getCurrentPosition(onSuccess, onError);
    } else {
        var content = document.getElementById("content");        
        content.innerHTML = "Geolocation is not supported by your browser!";
function onSuccess(position){
    var content = document.getElementById("content");        
    content.innerHTML = position.coords.latitude + ", " + position.coords.longitude;

function onError(error){
    var content = document.getElementById("content");        
    content.innerHTML = "Something went wrong..";

That’s really easy, right?

The scary part

The privacy part isn’t that scary, because the specs state that browsers must acquire permissions through a user interface. The scary part is, that it really works and is very accurate even though I’m on a desktop with no known hotspots nearby! After getting the results, I pasted them in Google Maps and they were only a few meters off. Why is it that while most geolocation services have been failing over the years, it suddenly works this good?

There is some documentation out there, but this documentation is very simplistic and doesn’t touch the internals.

The Pro HTML5 Programming book lists which sources can be used.

A device can use any of the following sources:

  • IP address
  • Coordinate triangulation:
    • Global Positioning System (GPS)
    • Wi-Fi with MAC addresses from RFID, Wi-Fi and Bluetooth
    • GSM or CDMA cell phone IDs
  • User defined

FireFox lets the Google Location Services assist them.

If you consent, Firefox gathers information about nearby wireless access points and your computer’s IP address. Then Firefox sends this information to the default geolocation service provider, Google Location Services, to get an estimate of your location. That location estimate is then shared with the requesting website.