Are the GPS coordinates a good source of entropy?
Probiably not.  If a hacker where to locate the device physicaly then the search space would be greatly decreased.  Even knowing the city (ip can give you that) might be enough.
Other similar sources with a higher entropy could be changes in lat and long, but those are most likely small.
You would most likely get better entropy using the accelerometer/gyrometer/magnomiter instead (if avaliable, I am assuming this is for a phone).
If you wanted lots of entropy, you could ask the user to give their phone a nice toss while poling gyro and acceleration.