Geo ranking doesn't work on specific attributes (i.e. City and Zip Code)

I’m having a problem understanding how the geo ranking actually works. We have hundreds of facilities that all have geoloc attribute, but typing a zip code or city does not return the closest locations based on that geoloc. For example, if I have a facility in Nashville, TN and I type the exact matching zip code 37208, it will not return anything but that facility, and not the several facilities that exist around Nashville.

How can I adjust my functionality so that it returns Facilities by proximity to a City or Zip Code query.