 
 extension MKMapView {
     ///The maximum length in meters of current viewport
-    func maxDimensionMeters() -> Double {
+    func maxDimensionMeters() -> CLLocationDistance {
         let topLeft:MKMapPoint = visibleMapRect.origin
         let topRight:MKMapPoint = MKMapPoint(x: visibleMapRect.origin.x + visibleMapRect.size.width,
                                              y: visibleMapRect.origin.y)

        }
    }

    /// Check that location is valid
    ///
    /// - note: This is a hack… 0.0;0.0 is a valid location. It is, however, also the default location
    ///  returned when coordinate acquisition fails… Apple really needs an 'invalid' flag on this class
    func isNonZero() -> Bool {
        return latitude != 0.0 && longitude != 0.0
    }


    //CLLocationCoordinate2DIsValid
}

extension CLLocation {

    }

    ///meters per pixel for current viewport
    func metersPerPixel() -> CLLocationDistance {
        return MKMetersPerMapPointAtLatitude(centerCoordinate.latitude) * visibleMapRect.size.width / Double(bounds.size.width)
    }
}
