docs: def to_esri_wgs_json(self):
          """
          Convert Viewbox object to a JSON string that can be used
          by the ESRI World Geocoding Service as a parameter.
          """
          try:
              return ('{ "xmin" : %s, '
                      '"ymin" : %s, '
                      '"xmax" : %s, '
                      '"ymax" : %s, '
                      '"spatialReference" : {"wkid" : %d} }'
                      % (self.left,
                         self.bottom,
                         self.right,
                         self.top,
                         self.wkid))
          except ValueError:
              raise Exception('One or more values could not be cast to a number. '
                              'Four bounding points must be real numbers. '
                              'WKID must be an integer.')