get Zoom Level
Returns the zoom value from range (0 - 20.0) The zoom level determines how "close" the map view is to the surface of the Earth. Higher zoom levels give a closer view. Zoom level values must be in the range returned by getMinMaxZoomLevel Zom level: 0 - world, 10 - city, 15 - street, 20 - buildings
Return
The zoom level value