I've forgotten a lot of my maths, but isn't the vertical scale always the same - and therefore different to the horizontal scale?
Richard On Fri, Jul 9, 2010 at 1:27 AM, Ben Last <ben.l...@nearmap.com> wrote: >> 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 > > > _______________________________________________ > talk mailing list > talk@openstreetmap.org > http://lists.openstreetmap.org/listinfo/talk > > _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk