Why does my tablet seem not to work properly as soon as I get out of my home? Why don't I see the map on the screen while I have a GPS on? Some keys to better understanding ...
First, a few words on GPS: the GPS system is a set of satellites operated by the U.S. military that enables - provided you have a suitable receiver - to know your geographical position at any point of the globe with 1-3 m (3-10 feet) precision. But it gives only your longitude latitude: GPS does not replace the map. It just replaces the pen tip that shows where we are. You must therefore possess independently a map of the area.
Map and GPS: two separate tools
GPS is not the only means for positioning: it is possible to obtain a fairly accurate position in urban areas from cell-tower antennas and wifi hotspots using triangulation methods. The advantage is that localization is much faster in these dense areas where GPS satellites are often masked by buildings. Indeed, while most tablets and almost all smartphones have a real GPS, these devices are set by default to get their position primarily from WiFi / 3G signals. Which is a good thing : while connected to one of these networks, they take the opportunity to download the map of the area.
Nice but ... all this does not work anymore outside areas of dense network coverage, ie in almost all areas where we like to practice outdoor sports (sea, mountain, air,desert ...)! In these areas, you need to use GPS positionning. Leaving WiFi ON can even be risky
As we have seen above GPS is not enough, you also need a map. And there is no miracle: for a tablet to display something on its screen, it must be present in its memory. The card needs to have been already loaded if you want to see it with no network connection.
A quality map is rarely free. This is the (low) price for security. Some applications allow to prepare your trip from home, downloading free maps in device's temporary memory. These applicationscan be used in the field, but you may still find yourself without a map :
- If you travel out of the planned area
- If the device's memory management decides without notice to remove this data to free up space.
Losing a map can have serious consequences ! It is recommended to use an app that downloads real maps permanently in memory.
In summary, to use a tablet or smartphones as a reliable location tool, you must:
- use a device with a real GPS
- use a specialized application, capable to load and display specific maps for your activity : topographic map, marine chart, aerial map ..
- Make sure to download the full map of the practice area before leaving