Why HTML5 Geolocation?

Why does H开发者_如何学PythonTML5 geolocation let you share your location? What is main purpose of using geolocation, as you can get the location with IP address as well. Is there any difference between these two methods?

I'm asking because geolocation requires the user's permission and also doesn't work on all browsers.

HTML5 GeoLocation tends to be much more accurate than IP-based GeoLocation.

IP-based GeoLocation depends on databases associated with ISPs to figure out where you are. This doesn't work well when your ISP services a very large area and gives out dynamic IP addresses. The address in one town today might be 100 miles away tomorrow. Furthermore, those databases are usually not updated frequently. If your ISP sells off blocks of IPs or moves them to a new town, the database may still incorrectly think you're somewhere else.

HTML5 location uses services provided by your browser to figure out where you are. If your computer has GPS built-in (such as on many mobile devices and some laptops), it will know exactly where you are. This makes it much more useful for webapps that have a navigation or location component. For devices without GPS, it can often provide a very good approximation based on nearby known wireless signals and other factors, such as tracing what routers your computer goes through when connecting to the internet. The exact implementation depends on the computer, what hardware it has available, and how the browser chooses to do things.

For example, when I check an IP-based location service, it says that I'm in a particular large city in the same general area that I live in, but it's actually about 50 miles away. When I use an HTML5 location based service to figure out where I am, it's only off by about 20 blocks.

If you're developing a webapp which needs location data, try using HTML5 GeoLocation if at all possible. Set up a fallback, so that if HTML5 location fails, you can use an GeoIP solution instead. This way, you will get optimal accuracy on supported browsers and devices, but will still have a solution in place when the HTML5 data are not available.

If you used the geolocation-javascript project from Google Code, you could use the following code:

//determine if device has geo location capabilities
if(geo_position_js.init()){
   geo_position_js.getCurrentPosition(success_callback,error_callback);
}
else{
   // use an AJAX request to look up the location based on IP address
}

Geolocation is a lot more precise than IP address, though both can be faked.

IP address just gives you country and general region.

Geolocation gives you:

• Geographic coordinates (latitude and longitude)
• Speed (assuming you're on a device that can measure this; most tablets and smartphones can)
• Altitude (this is also dependent on the device)
• Degrees clockwise from north (again, assuming the device supports this)

http://diveintohtml5.ep.io/geolocation.html has some good info on geolocation and the HTML5 geolocation API. Here's the W3C Candidate Recommendation.

Obtaining a user's location through the IP-address is by far not as accurate. The IP-address' location is mostly based on the location of the actual server, which can be requested. Often this is far away from the actual user's location, so it only provides the basic region.

HTML5 geolocation on the other hand is more precise, but the user's information is used to determine the location and often also speed along with some other things. This is based on the device's GPS if available, and otherwise on information entered by the user. Clearly this is way more accurate. Both methods can be faked though.

Getting location by IP address only gives a vague location (it is rarely any more accurate than to town, and often much less accurate than that, depending on your location and ISP).

It is also sometimes completely inaccurate: if I use a VPN to connect to my company network, I will show up as being at their office because I will have an IP address from the office, but I could actually be connecting from anywhere in the world.

HTML5 geolocation can be much more accurate -- if you have a GPS receiver in your device, then it is completely accurate, but even without that, in heavily populated areas it can get your position with an accuracy of 20 meters or less by mapping the local wireless network signals. And it doesn't matter how you've connected, it will always be accurate.

Because HTML5 geolocation is so accurate, it is considered a privacy risk, so the spec states that you must give permission before a site can use your gelocation data. Also, not all browsers or machines may be capable of providing the gelocation data. The website therefore must be able to cope with users who do not provide it, and cannot rely on it being provided.

IP address location doesn't have this kind of restriction because the location mapping is done by the server using publically available IP location mapping data. The end user cannot avoid giving out their IP address, so they cannot prevent the website mapping them using it.

So the two are completely different.

The major difference that you will see is the accuracy. IP addresses only give you a very general idea of where someone might be... Geolocation will tell you exactly where they are. To read more on geolocation go here, and a demo of how accurate it can be can be is found here

HTML5 geolocation gives the client (browser) the possibility to provide the location information of the machine. This is potentially orders of magnitude more accurate than IP location. For example, the client could have actual GPS hardware installed, or be able to triangulate the location by GSM or WiFi spots. Location by IP on the other hand is very rough and somewhere between not always accurate and misleading.