If you try the geoip command you should see fields for city, country_code, country_name, postal_code, region_name, etc
just do your search like:
my_search | geoip ip_address
In the search app and you should see the fields on the left hand side. After that you can use stats or whatever else you like to group by one of those fields.
By the way, there is some docs on the google maps app when you are in the app, click on the about "About Google Maps for Splunk" link in the upper right hand corner.
