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#1 2016-01-17 18:30:24

Black-Eyed Lion
Member
Registered: 2010-09-17
Posts: 6

Scale of the zoom levels

Dear OSM Forum, there is a table of the scales of the different OSM zoom levels: http://wiki.openstreetmap.org/wiki/Zoom_levels. I wonder about the values for the meters per pixel. When I download a StaticMap or load a map on osm.org in zoom level 14, the image has a scale of 6 to 7 meters per pixel.

E.g. on this map

http://www.openstreetmap.org/#map=14/40.6865/-74.0321

the distance from Richard Street Station (on the top left) to High Street Station (on the top right, same vertical position) is 1041 pixels on my screen. The real distance is about 7200 meters, which yields 6.9 meters per pixel. What am I doing wrong? Is there a way to query the scale when loading a StaticMap? Thank you for your help!

Last edited by Black-Eyed Lion (2016-01-17 18:31:50)

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#2 2016-01-17 21:59:49

hadw
Member
Registered: 2014-09-02
Posts: 1,075

Re: Scale of the zoom levels

If you look at the formula, the scale depends on the latitude.  For the example you give, the result is 7.239 m/pixel, based on a spherical earth.

At the scale you quote, the horizontal size of a tile is 1.3184 minutes of longitude (rounded), independent of latitude, the vertical scale is set to match, and the tiles are 256 pixels square.   Cross checking.  1 nautical mile is 1 minute at the equator.  1nm ~~ 1 statute mile.  Allowing for latitude, 1 minute is going to be close to 1 statute mile.  1760 yards / 256 is 6.9 yards. 1 yard ~~ 1metre.

You can calculate the scale from numbers found in the URI.

Last edited by hadw (2016-01-17 22:00:56)

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#3 2016-01-18 23:57:11

Black-Eyed Lion
Member
Registered: 2010-09-17
Posts: 6

Re: Scale of the zoom levels

Thank you, that helped. I clarified the usage of the meters per pixel values in the wiki.

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