docs: def distance_to(self, point, unit='km'):
          """
          Calculate distance in miles or kilometers between current and other
          passed point.
          """
          assert isinstance(point, GeoPoint), (
              'Other point should also be a Point instance.'
          )
          if self == point:
              return 0.0
          coefficient = 69.09
          theta = self.longitude - point.longitude
          unit = unit.lower() if unit else None
  
          distance = math.degrees(math.acos(
              math.sin(self.rad_latitude) * math.sin(point.rad_latitude) +
              math.cos(self.rad_latitude) * math.cos(point.rad_latitude) *
              math.cos(math.radians(theta))
          )) * coefficient
  
          if unit == 'km':
              return utils.mi_to_km(distance)
  
          return distance