GPS is not working

GPS stands for Global Positioning System. This is a satellite-based navigation system that provides location information. GPS is available worldwide.

To optimize the location capability of your phone, A-GPS is a common feature in mobile phones. It supports the regular GPS system by using extra network resources to strengthen the connection in areas where the GPS signal is weak. This service may cause your phone to use more data than usual.

It is important that you activate EPO (and also the option ‘Auto Download’ in the EPO options) at least once so that the satellite almanac updates. EPO (Extended Prediction Orbit), is an extra GPS feature that downloads a file to help the device locate GPS satellites quicker and reduce the time to establish a connection. Please activate this option at least once to let your Fairphone 1 update.

There are also a couple of things you can do to improve your GPS signals:

Activate A-GPS and EPO
You can activate A-GPS and EPO here: Settings → Location access → GPS satellites (tap the text) → Check A-GPS and GPS EPO assistance

Download the newest EPO files
You can download EPO files here: Settings → Location access → GPS satellites (tap the text) → EPO settings → Download

Please note
The download might fail several times. If it doesn’t work, try again at a later time.

Set NTP server
To sync quickly to the satellites, you should always connect to your nearest NTP server. You can do this yourself by editing gps.conf in system/etc, but is recommended to download the FasterGPS app. Once installed, grant superuser access and set your region and country. After this the correct files will be written and it should help getting a proper GPS connection.

For more technical information check this developer's forum; it contains useful guides.