[OSM-talk] scale question

Richard Mann richard.mann.westoxford at googlemail.com
Fri Jul 9 10:51:15 BST 2010


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.last at 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
>
>
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