Maps, GPS and 3G/4G: What You Should Know

(Update : April, 29th 2020)

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. This positioning network (GNSS) has been joined the last decades by other networks, Russian GLONASS, Chinese BEIDOU, and recently European GALILEO.

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 use a combination of WiFi and cellular signals to assist GPS, for example in urban "canyons". 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 only GPS positionning.

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 stored in mass storage. The map needs to have been already downloaded if you want to see it with no network connection. 

A quality map is rarely for 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 applications can be used outdoor, 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.

- If you travel out of the planned area 

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.