[OSM-dev] Re: [OSM-talk] Simple GD rendering

[Oliver White]

Any other ideas on map projections to use?

As far as I can tell, there are certain properties that you'd like to have on 
a map, and different projections each fulfil one or more of them:
 * Accurate distances
 * Accurate angles and small shapes
 * Accurate areas
 * Straight lines are straight on the map
 * Lines of constant bearing are straight on the map
 * Different map sheets fit together nicely
 * Suitable for large areas
 * Suitable for various locations around the world
 * Doesn't disappear completely in certain areas (e.g. at high latitudes like 
Mercator, or in the middle of the Isle of Man like OSGB)
 * Doesn't go crazy around Norway (like UTM) or require special-cases (like 
UTM at the poles)
 * Easy to calculate, especially if you're doing it millions of times per map

Does anyone have particular favourites?  Personally I've found most of them to 
be lacking in significant ways, but would be interested to know what's seen 
as "a good idea" for street maps.

I rather like the idea of an orthographic projection centred on the map (like 
a "top-down" view from space) although that's still got loads of distortions

OJW

http://almien.co.uk/Links/Science/Cartography/Projections/


On Monday 15 May 2006 03:57, Hamish wrote:
> > Just playing with a PHP/GD renderer for the OSM data - it's all based
> > on  planet.osm, so nothing more recent than April.
> >
> > http://almien.co.uk/OSM/Viewer/
>
> You might want to scale local maps in a map projection like UTM that is
> a bit more equal-area than Plate Carrée. Or just scale x-axis by
> cos(lat). That way you can make accurate scale bars etc. Maps spanning
> more than 200km or so should probably continue to use Plate Carrée
> (1lat : 1lon).
>
> Hamish