[OSM-dev] Slippy Map Elevation Overlay

Graham Jones (Physics) grahamjones at physics.org
Tue Apr 28 22:30:04 BST 2009

I sometimes think that the main slippy map has a bit too much plain white,
especially in undeveloped places where there are not many roads such as the
Pennines or North Yorkshire Moors in Northern England - I keep wondering if
this is an un-mapped area, or if there is nothing there....

The cycle map is very good with shaded elevation contours, but the main
osmarender and mapnik maps do not include this.
I would like this sort of shading to be available for the main map too, but
I am not convinced that rendering it into the tiles is good, because
sometimes those extra colours or contour lines are a distraction, so it
would be nice for the user to be able to switch them off.

I wondered if there is any reason why we could not create an overlay of
elevation information (contours and or shading) that could sit on top of the
main map as a user selectable leayer?

I have had a quick go at http://maps.webhop.net/srtm.html.  It sort of works
- the high ground stands out, and you can see the shape of the ground, and
you can switch the overlay off and on.  It does not work that well as an
overlay though because it is not really transparent enough.  I find that
sometimes the transparency works quite well and you can see the map
underneath, and others it is practically opaque.

I struggle a bit with javascript and openlayers and wondered if anyone could
suggest how I could sort out the opacity problem a bit better?
Maybe the main map should use a transparent background, and use the
elevation data as the base layer with the map as the overlay?



Dr. Graham Jones
Hartlepool, UK
email: grahamjones139 at gmail.com
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