Calculate distance in miles or kilometers between current and other
        passed point.

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