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I don't understand why do mobile map services require turning WiFi or 3G on to show my current place.

Most of mobiles have GPS and I turned it on. But they still require WiFi. Is there someone to explain this technically?

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up vote 4 down vote accepted

Apart from the fact that you need to get your map data somewhere (i.e. over a 3G or WiFi data connection), the current answers miss the most important point:

To obtain your precise location.

GPS is very precise once it acquires lock on enough satellites. However, more often than not, this takes a while, especially with small receivers or in a city (where huge buildings obstruct the view to the sky). In that case, other methods can be used to get a more precise location (or a rough estimate of it) before GPS is used to track your device.

In fact, there exist databases which allow you to query your location simply based on the WiFi networks you're currently seeing. Or, your 3G cellphone connection could be used to triangulate your position from nearby cell towers (see Assisted GPS).

This is why your phone prompts you to activate WiFi or 3G.

More info: Location-based services and mobile phone tracking.

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Personally - when I use IP based location for my own device and network the answer is of by approx 100km. so I don't think this is the main issue. If anything you should state that its "To obtain your unprecise location" if satellite info is not available. – epeleg Jun 9 '12 at 8:58
I clarified that part, but I think this really depends on where you are. I used to get initial precisions within less than a kilometer in most cities, even with 3G. This is taking my Android phone as a reference. Results may vary of course. – slhck Jun 9 '12 at 9:01
ture. results vary. But IMHO still for almost any real app the reason would not be that but the need for data from the web (maps/user prefrencess/app data from a database/friends information etc.) as I stated in my answer. – epeleg Jun 9 '12 at 9:16
Hm. I used to cache my (vectorized) Google maps all the time when I was using the phone abroad. And they would use up a few megabytes maybe. I could cache everything within 10 square miles and the phone would still prompt me to turn on WiFi, explicitly saying that it would speed up GPS lock – even though I already had the map data fully cached. I do get your point, but I guess the OP is already aware of that. – slhck Jun 9 '12 at 9:24
@epeleg well, slhck is right. That's my intention. I think that because my English was poor, you catched a mis-point. My fault. – Benjamin Jun 9 '12 at 12:38

Because usually they won't just display the GPS coordinates of your currrent location but display a map or require some other info from the WEB.

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But what if I download all map to my mobile local storage? What's your some other info? – Benjamin Jun 9 '12 at 8:17
Unless you are talking about some very specific and local application It would notmally not be possible to keep the maps locally in good enough resolution. also It would mean that changes would not be reflected in the app. "other info" could range server side saved user preferences of different sorts to any other information - depending on the app itself (like traffic jam info). – epeleg Jun 9 '12 at 8:23
I want to clarify: It is not impossible to write an app that comes preset with an image of a map of your own village for example and will show you your location on that map without the need for a web connection. But It would not be a common scenario as most app developers would prefer to write more general code and use API's like google maps that will place the said markers on the map based on coordinates without the need to do the math yourself. – epeleg Jun 9 '12 at 8:27
  • Your phone lacks the storage for high resolution mapping of the whole of planet earth.
  • When you download the app from the app store, you don't want to wait days while your phone downloads high resolution detailed mapping of the millions of square kilometers you'll never look at.
  • You probably like to have up-to-date maps that include recent changes. It is more efficient to show you latest info from mapping servers for the area you are looking at than to continually be sending your phone updates for areas you may never look at.
  • Vector data for planet earth is large. Now consider high-resolution satellite/aerial photography (which is an option in google maps at least)
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