code: private static boolean isValueAValidGeoQuery(final Object value) {
          if (value instanceof DBObject) {
              String key = ((DBObject) value).keySet().iterator().next();
              return key.equals("$box") || key.equals("$center") || key.equals("$centerSphere") || key.equals("$polygon");
          }
          return false;
      }
docs: this could be a lot more rigorous