[OSM-talk] contours on main map

[Robert (Jamie) Munro]

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Steve Hill wrote:
| On Thu, 8 May 2008, Robin Paulson wrote:
|
|> alternatively, are there any world wide maps out there with contours
|> and osm data, that update regularly?
|
| The cycle map and the piste map both have contours for selected areas.
| I'm generally doing monthly updates to the piste map data.  As far as I
| know, no one is serving contours for the whole planet - there are a
couple
| of reasons:
|
| 1. The SRTM3 dataset for the whole planet is pretty huge once it has been
| processed into contour lines and put into PostGIS (probably about half a
| terabyte).
| 2. It isn't as simple as just rendering the same contour lines everywhere
| - for example, the piste map uses much wider spaced contour lines than
the
| cycle map because the terrain is (generally) more mountainous.  To make a
| global contour map you would need to make the renderer vary the number of
| contour lines used depending on how mountainous the terrain is.

Why not draw contours in a light shade, then draw every 10th contour
line in a darker shade. On a mountain, the light shades may just blend
into the terrain of the mountain, leaving the dark lines picking out the
~ contours of mountain itself. If neccesary, you could have several
levels of colour for different powers of 10.

What would be nice is to separate the map into a background layer, with
areas, and a transparent foreground layer with the roads, so that a
contour layer can be slipped between the two at the openLayers level.

Robert (Jamie) Munro
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