Using this:

https://cloud.google.com/compute/docs/load-balancing/http/ba...

The load balancer expands variables to empty strings when it cannot determine their values, for example for geographic location variables when the IP address’s location is unknown, or for TLS parameters when TLS is not in use.

Geographic values (regions, subdivisions, and cities) are estimates based on the client’s IP address. From time to time, we update the data that provides these values in order to improve accuracy and to reflect geographic and political changes.