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HTML5: Up and Running by Mark Pilgrim

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Choices! I Demand Choices!

Some popular mobile devices—like the iPhone and Android phones—support two methods of figuring out where you are. The first method triangulates your position based on your relative proximity to different cellular towers operated by your phone carrier. This method is fast and doesn’t require any dedicated GPS hardware, but it only gives you a rough idea of where you are. Depending on how many cell towers are in your area, this “rough idea” could be accurate to as little as one city block or as much as a kilometer in every direction.

The second method actually uses dedicated GPS hardware on your device to talk to dedicated GPS positioning satellites that are orbiting the Earth. GPS can usually pinpoint your location to within a few meters. The downside is that the dedicated GPS chip on your device draws a lot of power, so phones and other general-purpose mobile devices usually turn off the chip until it’s needed. That means there will be a startup delay while the chip initializes its connection with the GPS satellites in the sky. If you’ve ever used Google Maps on an iPhone or other smartphone, you’ve seen both methods in action. First you see a large circle that approximates your position (finding the nearest cell tower), then a smaller circle (triangulating with other cell towers), then a single dot with an exaction position (given by GPS satellites).

The reason I mention this is that, depending on your web application, you may not need high accuracy. For ...

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