[Android Apps and Games] taob:
That is correct. Pre-cached map data is automatically cleared after 10 days. You can verify which areas are still on the phone by going to Settings -> Cache Settings -> Pre-cached map areas.

---------- Post added at 08:18 PM ---------- Previous post was at 07:52 PM ----------

There are several aspects to the use of the Maps and Navigation apps. Perhaps some people think they are one and the same? Or they do not distinguish between "positioning" and "route-finding". Even thinking just in terms of "GPS", it is a bit more complicated than what most people realize.

When you tell Google Maps to pre-cache map tiles, it does exactly that: download the database of vector information used to draw roads, building outlines, building 3D data, geographical features, place names, street names, etc. That way, it can display visual map graphics without having to download the data again. It is useful not only when you are offline, but also to save on network data usage.

Using your GPS radio, you can determine where you are on that map. If you are moving, the app can also derive what direction you are travelling. Thus, it knows whether to draw a blue circle or a blue arrowhead, and where to place that on the map.

However, there will even be some instances where GPS functionality will be limited if you do not have a data connection. This has to do with something called the "GPS almanac". It is an up-to-date list of the locations of each GPS satellites in the sky. After all, you need to know where the satellites are before you can figure out where you are! Because the satellites move relative to the earth, occasional updates must be downloaded to the GPS device. And guess how a phone does it? Over its data connection!

It is possible to download the GPS almanac over the GPS signal itself, but it is an extremely slow process, and I'm not entirely sure Android phones support that. So if you do not use GPS often, and you fire it up one day without an active data connection, you might notice that it takes a very long time to get a position lock (or never at all).

Now back to the map data: I don't know if the vector data used by the Google Maps app is shared with the Google Navigation app. If it is, then the best you will get without a data connection is GPS positioning. The route-finding mechanism (i.e., when you ask for driving, walking or transit directions) is performed by Google's servers. While it is certainly possible to write route-finding software for the phone, it is not included in the GMaps app because the assumption is that your phone is always online.

Same goes for any voice searches for places and locations. The waveform of your speech is sent to Google's servers for analysis, and the text is sent back to your phone. The phone then sends the text back out to a different set of servers to perform the search, with the results sent back to your phone.

So in the end, just being able to download map tiles does NOT mean Google Maps and Google Navigation can be used entirely offline. The purpose of this feature is to speed up Maps operation, and to save on network bandwidth. Map tiles are only a small requirement for functionality. If you need full offline capabilities, you'll have to download a third-party app.

Finally, don't forget that pre-caching map tiles is a Labs feature, which means it might be buggy, and it might disappear without notice. :)