> > At 09.07.2010 01:19, Mostafa El-ashram wrote: > > Please could you tell me how to determine the scale of a map on open >> street maps >> > The TMS co-ordinate system (OSM, Google Maps, NearMap, Bing Maps, etc) use a Mercator projection; you'll find it referred to as "cylindrical Mercator" and "spherical Mercator". http://en.wikipedia.org/wiki/Mercator_projection http://mathworld.wolfram.com/MercatorProjection.html http://www.sharpgis.net/post/2007/07/27/The-Microsoft-Live-Maps-and-Google-Maps-projection.aspx
To derive the scale in metres per pixel at a given latitude and zoom level, you can use this (JavaScript, which uses radians for trig): metresPerPixel = Math.abs(156543.04 * Math.cos(latitudeAtCentreOfMap * nml.PI / 180)) / Math.pow(2, zoomLevel); See http://msdn.microsoft.com/en-us/library/aa940990.aspx for a reference. Cheers b -- Ben Last Development Manager (HyperWeb) NearMap Pty Ltd
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