Is there a way to completely switch off GPS or deny apps access to it?
Even though all three checkboxes in
Settings -> More -> Location Services are unchecked and the button in the notification drawer is off, apps are still able to determine my location using GPS.
Access to my location checkbox is not completely without effect, it does prevent Google Maps from showing my location. I noticed that in this demo application the "fused" location stops working but the "GPS" location still works. I further noticed that in GrabTaxi, a taxi hailing app, the map is disabled, but it is still able to search for "nearby places" (with much better accuracy than GeoIP).