[OSM-dev] map projection and scale distortion

Tom Hughes tom at compton.nu
Wed Apr 16 18:24:51 BST 2008

In message <1e68ba6b0804161009y6df037bbwf7a31f706a65895a at mail.gmail.com>
          "Raghu Ram" <raghuram.nadiminti at gmail.com> wrote:

> Also I see that Mapnik osm.xml (style sheet) filters on the basis of scale
> denominators. But assuming that the projection suffers some scale distortion
> how could one ensure that the same style is applied all over the world at a
> particular zoom level. I am trying to develop a WMS SLD ( projection is
> EPSG:4326 ) and facing issues with scale denominators and zoom levels.
> Please help me out how OSM handles this issue.

I think that's really a question for the mapnik list, but the simple
answer is that we don't do anything clever to handle it.

The difference in scales between zoom levels is probably large enough
that it isn't really an issue though if you set a reasonably wide range
of scales for a feature rather than trying to pin down an exact scale.

You will probably notice that osm.xml is all over the shop when it
comes to specifying scale values - there is no real fixed set of values
that are used throughout to target particular zoom levels.


Tom Hughes (tom at compton.nu)

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