gistfile1.py

class Location(Document):
  structure = {
    "ll" : validate_coordinates,
    "street" : ...
    ...
  }

class Venue(Document):
 structure = {
   "location" : Location.validate,
   "name" : unicode,
   ...
 }

 @property
 def location(self):
   # should be cached
   return Location(self['location'])

In fact that isn't even really necessary... it's just a list so we could override the validate() method on the Venue and implement the check there...