Igor,
Sorry for resurrecting this old thread, but I've been working on deploying Nginx, and I noticed that the GeoIP City module is missing a couple of variables that are set by the equivalent mod_geoip module for Apache.
The variables in question (as set by mod_geoip) are:
GEOIP_ADDR
GEOIP_REGION_NAME
GEOIP_DMA_CODE
GEOIP_AREA_CODE
I'm not certain what information you'd need to add these to the module, but I'd love to see the GeoIP module to be as inclusive as the Apache equivalent.
Let me know if there's any information you're lacking and I'll do my best to dig it up.
Thanks!