HTML5 Geolocation API – how accurate is it, really?

If you are a developer building applications that require location information then you need to know what is really possible with the HTML5 Geolocation API and not a bunch of hype. The blog post attempts to give you some insight into how it works with desktop and mobile browsers as well as having a greater appreciation for what is and what isn’t possible. I’m going to show you that accuracy depends on many factors, some of which are beyond your control, and at best the location information returned by the API is just an approximation.

[Editors note: as of June 29th, 2013 Part 2 of this post is now available]

Most common use case. For the most part, HTML5 Geolocation works just fine in dense urban areas when you are stationary with your laptop or smartphone Wifi turned on. This is the use case most commonly cited when questions are asked about accuracy. This makes sense because urban areas have many public and private Wifi routers and cell phone towers are typically closer together. As you’ll see, HTML5 uses these and other methods to pinpoint your location. However, it’s not always that simple and below are some other use cases that you should take into consideration.  

How does the API work? Depending on which browser you are using, the HTML5 Geolocation API approximates location based on a number of factors including your public IP address, cell tower IDs, GPS information, a list of Wifi access points, signal strengths and MAC IDs (Wifi and/or Bluetooth). It then passes that information to a Location Service usually via an HTTPS request which attempts to correlate your location from a variety of databases that include Wifi access point locations both public and private, as well as Cell Tower and IP address locations. An approximate location is then returned to your code via a JavaScript callback.

As an example to show you what type of information is sent to a Location Service, I did some basic testing with Firefox 11. Firefox uses Google’s Location Service. On a related note, as far as I can tell with Firefox 11 it isn’t passing cookies any more where in Firefox 3.6 they use to pass a user ID token.

Firefox 11 browser sends queries to https://maps.googleapis.com/maps/api/browserlocation/json? The example results have been obfuscated, but by looking at it you should get the idea of what content is being sent:

GET /maps/api/browserlocation/json?browser=firefox&sensor=true&wifi=mac:01-24-7c-bc-51-46%7Cssid:3x2x%7Css:-37&wifi=mac:09-86-3b-31-97-b2%7Cssid:belkin.7b2%7Css:-47&wifi=mac:28-cf-da-ba-be-13%7Cssid:HERESIARCH%20NETWORK%7Css:-49&wifi=mac:2b-cf-da-ba-be-10%7Cssid: ARCH%20GUESTS%7Css:-52&wifi=mac:08-56-3b-2b-e1-a8%7Cssid:belkin.1a8%7Css:-59&wifi=mac:02-1e-64-fd-df-67%7Cssid:Brown%20Cow%7Css:-59&wifi=mac:2a-cf-df-ba-be-10%7Cssid: ARCH%20GUESTS%7Css:-59 HTTP/1.1

Which location service do browsers use?

Not all Geolocation services are the same, and they certainly don’t all use the same algorithms and exact same databases. Because of this the results typically vary across browsers that use different Geolocation services.

Here’s my best attempt to document which Geolocation service each of the major browsers are using. I haven’t done any definitive testing however I do know from experience that different browsers and even different laptops for smartphones will return different locations when tested from the exact same location. Some location services are better in some cities and others are better in other cities. I haven’t come across a definitive list, most likely because the information is constantly being updated. I’ve included a link to a demo application at the bottom of this blog where I encourage you to also test the API against different browsers.

  • Chrome uses Google Location Services.
  • Firefox on Windows uses Google Location Services.
  • Firefox on Linux uses GPSD – http://catb.org/gpsd/. I’m not sure if this includes Android. I haven’t had a chance to test it yet.
  • Internet Explorer 9+ uses the Microsoft Location Service.
  • Safari on iOS uses Apple Location Services for iPhone OS 3.2+.
  • I’m not sure what Safari on Windows uses. With all the public distrust between Apple and Google, I wouldn’t be surprised if Safari on Windows also uses Apple’s Location Service, but I haven’t found any documentation to verify this and I haven’t tested it.
  • Opera uses Google Location Services. On a related note, I’ve also noticed that mobile Opera on Android accesses the GPS. This is something to consider from a battery usage standpoint.

Not all browsers support HTML5. It’s important to note that not all browsers support the HTML5 Geolocation API, for example Internet Explorer 8. The HTML5 Geolocation API is built into the browser and is accessible using JavaScript methods that access the navigator object. In order to work it requires HTML5 support in the browser. You can research whether or not a particular browser supports Geolocation by going here: http://mobilehtml5.org/ or http://caniuse.com.

Additionally, if a user has disabled JavaScript for some reason, then your Geolocation app won’t work in their browser. JavaScript code is required to access the API.

HTML5 Geolocation requires an internet connection. If you lose your internet connection then you won’t be able to access the Location Service. With no internet connection most browsers will not return a location. Sometimes you can access a cached location that is stored in the browser by the API. But, that cached location is the last valid location that was calculated by the API.

Is Wifi turned on or off? If Wifi is turned off on your phone, desktop machine, laptop or tablet , the Geolocation API service will try to find your location by other methods which include your public IP address, Cell tower ID triangulation or GPS. Public IP addresses databases usually return a location for your internet providers Point of Presence or PoP. Furthermore, some internet provides offer rotating IP addresses. So you get to use one IP address for a particular time period such as 48 hours and then you get a different one. So a Public IP address is usually only good enough to locate you to a particular City, or a general area of the City, or a Country depending on where you are in the world.

As for Cell Tower IDs it depends on what type of information your particular phone and Telco Carrier provides to the API. Some smartphones only return information on the current tower that the phone is pinging, which obviously makes triangulation very difficult and decreases accuracy to within a radius around that tower.

I’ve noticed that the native Android browser is significantly less accurate without Wifi. Without it I typically see accuracy numbers in the 1000+ meters range. As soon as I turn Wifi back on and I’m in a neighborhood or downtown area, the accuracy drops to less than 75 meters almost instantly.

Are they in a rural or urban location? Granted the vast majority of users will be in urban locations. However if you have requirements for users traveling outside of urban areas then this section applies to you. Geolocation in rural areas is significantly less reliable. If Wifi is turned on but the user is not near any Wifi access points, then the Geolocation service will also attempt to fallback to the other methods mentioned above.  Triangulation can be much more difficult in rural areas where towers are spread further apart, and for browsers that don’t use GPS the accuracy will suffer significantly.

Are you moving or stationary? Being stationary in an urban area offers far better accuracy with the Geolocation API than when you are moving. On my native Android phones it’s rare to get an accurate reading while driving around town. Occasionally a sporadic result would be returned when you stop at a light. To date, I have never gotten a valid reading while driving on a highway at speeds over 50 mph.

Is a VPN turned on? If a VPN is turned on, then the location will resolve to the VPN’s public IP address. For example, a user in Denver is logged into the company VPN which host is hosted at their headquarters office in a suburb of Dallas, Texas. The HTML5 Geolocation API will resolve the location to the headquarters public IP address in Dallas and not the user’s actual location. Quite a few corporate users have VPNs for security reasons.

Custom Geolocation as a fallback? Depending on your requirements you may want to implement your own IP Geolocation using a company such as IP2Location. Or use a third-party Geolocation service, such as Skyhook, as a fallback. Remember IP Geolocation only returns locations to a City or an area within a City. So, if you need more accuracy than that for your application, then don’t bother with this approach.

The downside to custom IP Geolocation is that this requires writing a server-side service to grab the browsers IP address. All server-side languages such as PHP, C#.NET, Java and JSP support these capabilities. You also have to subscribe to another service that lets you query their database by IP address and get a return value of an approximate location. There is no current way to get this information from the browser, on the client-side, using JavaScript.

HTML5 Geolocation doesn’t meet my requirements, what do I do? If you have critical requirements for gathering more precise location information than the HTML5 Geolocation API is capable of delivering then I’d recommend building your application using a native API such as Android or iOS.

How can I test this? You can test HTML5 Geolocation in different browsers using a test application that I built. I recommend trying it on different browsers and comparing the results yourself:

http://andygup.net/samples/html5geo/

References

Mozilla FAQ

Mozilla Developer Network

Google Location Service

W3C Geolocation API in IE 9

Safari Developer Library

Opera Geolocation

IP Geolocation

W3C – Privacy of Geolocation Implementations

Apple Q&A on Location Data

The 1 Minute Primer for HTML 5

HTML 5 is getting a lot of press these days and I get a constant stream of questions from many non-techies, as well as developers, asking me to explain HTML5 in layman’s terms. So here it is.

HTML 5 is really a combination of three things: HTML, CSS and JavaScript. When all three of these technologies work together in a web browser then you have an HTML5 application. Period.

Why should we care about HTML 5? HMTL 5 brings many long awaited enhancements that make it easier for web developers to build more complex applications. More importantly, HTML 5 is being adopted by the major browser vendors: Google, Microsoft, Mozilla and Apple and this adoption is making it possible for developers to take advantage of the latest web technology that are built into web browsers.

How is HTML 5 “built into a web browser”? Web browsers have to interpret a web page first, and then display the content for you. Browsers contain logic that let’s them parse a pages’ code, and that code provides instructions for the browser to do certain things. Behind the scenes, in fact, the page you are looking at is built using code. It’s the browser that interprets the code and displays it in a way that makes sense to you. If you haven’t ever seen web page code then you can usually select View > Source on your browsers tool bar. Cool, right?!

HTML 5. HTML 5 is the latest version of the Hypertext Markup Language (HTML) specification which has been around in various forms since approximately 1991. HTML is a tag based language that defines the meaning and placement of elements of a web page. For example, a <button> tag defines a clickable button on a web page.

Cascading Style Sheets (CSS). Cascading Style Sheets, or more specifically CSS version 3 (a.k.a CSS3), provide the ability to apply styling to HTML elements. An example of styling would be to change the color of an HTML <button> from grey to green, as well as defining where on a web page it will be visible such as the top left corner.

JavaScript. JavaScript, which is really the meat behind HTML 5, is a type of programming language that lets developers implement actions within a web page. An example of an “action” would be when a web page visitor clicks a button that loads a picture. So, HTML defines the <button>, CSS styles the button, and JavaScript handles the action behind the scenes by retrieving the picture and then telling the browser how to display it for the end user.

This all sounds great, are there any downsides? Yes. First, HTML 5 is a standards-based specification that is still a work in progress. The specification and all its’ associated parts won’t be finalized for some time, possibly years. The good news is that browser vendors are keen to adopt this standard as much as possible. Second, implementation across different browsers isn’t 100% consistent. The good news is that there are tools and online resources to help developers work around many of these problems. Last, older versions of browsers (e.g. Internet Explorer 7 or 8, older versions of Safari, etc) don’t support HTML 5. There are strong campaigns under way to educate people to upgrade for security, performance and viewing experience.

So, there you have it. That’s a cursory pass at HTML 5 and I hope this post helps. I’ve added a few links at the bottom if you want to learn more about it.

Learn More:

 HTML5Rocks.com – includes information on features, tutorials and great slide decks.

w3Schools.com –  includes live “Try it” samples that let you explore the functionality.

W3C HTML 5 Specification –the World Wide Web Consortium is the group that writes the standards. If you are a techie, this is “the” specification that the browser vendors base their functionality on.

Major public web sites miss the mark on using advanced web technology

As a developer I notice things about web sites that the average person wouldn’t think twice about. I also know that the level of technology that’s available to build user interfaces is well beyond what we had in the early 2000’s. And, the ability to build amazing, user-centric interfaces is as easy as ever. But, I’m always perplexed that most major web sites today incorporate very little of this technology in their full functionality web pages.

So, I’ve been doing an informal survey for the past month and my list includes major news sites, airline web sites and retailers. The vast majority of them aren’t much easier to use than they were five years ago with a great a selection of hyperlinks, tabs and full page refreshes. For the fun of it I decided to travel back in time using an internet time machine call the Wayback Machine and compare some of these sites to their predecessors. I challenge you to do the same.

I have a few suspicions as to why this is happening, or not happening as the case may be. First, plug-in based technology such as Adobe Flex and Microsoft Silverlight typically require some amount of time to load the initial payload into the browser. Sometimes you can create highly optimized or lazy-load packages, but it challenging. It’s rare to find one of these apps that load in the sub-second timeframe required in today’s hyper-competitive environment. The general impression is that the longer your page takes to load, the fewer the visitors you will have. So most major websites code is mostly made up of HTML, JavaScript, jQuery and CSS which most browsers have gotten really, really good at parsing extremely fast.

Second, it’s challenging to build Flex and Silverlight websites so that web crawlers can read text-based content. This seems fairly academic. If you can’t effectively index the content of your site, then potential visitors can’t search it via external search engines such as Bing and Google. Period.

These two items alone may explain why visually spectacular interfaces are limited to small portions of most public websites such as video plug-ins, or just specific sections of a much larger website. Where these more advanced interfaces typically reside are in back office applications where functionality trumps the need for millisecond application load times. There are some very cool exceptions for consumer apps such as the end-user experiences shown Mini Cooper’s build your own car online website. Yet, unfortunately for us as consumers, these are few and far between as consumer companies cater to the vast hunger for ever faster page load times.

The good news for advanced web technology in consumer apps is I’m seeing a large opening with mobile deployments. The plug-in technologies now have the capability to allow you to deliver visually enticing experiences across a wide array of devices. And this can be done, for the most part, without the tedium of worrying about all the vast nuances of different browser types and versions. Plus there is a bonus: the application is manually loaded and ready to go on your device minus the on-device load time when you turn on the app. I’m seeing some really innovative uses of the technology in what I call focused solutions, or applications built for a very specific purpose. Unfortunately most are in commercial beta and I can’t link to them. But, you’ll see them soon in an online marketplace right at your fingertips.

References:

Mobile Development with Adobe Flex 4.5

Silverlight for Windows Phone

Flex.org Showcase

Study: Consumers abandon slow loading websites (April 2010)

Let’s make the web faster (Google, May 2010)