Location comes from the sysLocation OID when you add a device. If you know your device should have a location reported, you can go to that device's manage page and perform an 'Import Settings' which would refresh name, location, and contact details.
To test, you can login to your AMP CLI and run a test walk to your controller:
# s2w <ip of controller> <community string> sysLocation
Example:
[root@airwave mercury]# s2w 10.10.10.100 public sysLocation
SNMPv2-MIB::sysLocation.0 = STRING: Server-Lab
The above helps for switches and controllers. For APs, you want to go to the AP's manage page, and then update the 'Location' field (under Settings box).