The GPS connection indicator is not part of the D7100 control panel display icons. The GPS connection indicator can only be displayed on the D7100 LCD screen, right below the Metering icon. See page 11 and page 152 of the D7100 manual. You can view this information by pressing the I-button on the d7100 about 2 times.
You will need to connect the GP-1A to the D7100 with the supplied CA-90 cable. If there is communication between the GP-1A and the D7100, you will see a flashing red light on the GP-1A. Once GPS signal is acquired, the flashing red light on the GP-1A turns green.
You can access the GPS option in the camera by pressing the Menu button, select Setup Menu, then select. GPS.
Verify position information before taking a picture.
If your issue persists, please contact Nikon Support for assistance.https://support.nikonusa.com