[OSM-talk] displayed width of roads
bvh-osm at irule.be
Mon Feb 18 15:10:03 GMT 2008
On Mon, Feb 18, 2008 at 11:51:38AM +0000, Steve Chilton wrote:
> > What a professional road atlas would do here is very likely to exaggerate
> > the junction so that it makes sense given the width using to render the
> > roads. Doing this algorithmically is hard, but probably not impossible.
> that sounds very bad, ugly and wrong on many levels.
> whether it's mapped as 'exaggerated' or algorithmically altered later,
> i can't see the point. if there's room in reality for the roads to
> exist without overlapping, then there's no reason the map can't
> reflect that
Sure there is a reason : the legibility of small features.
Assume a standard motorway map with scale 1cm:2km. A road that is 20m
wide would show up as 1/100cm = 0.1mm. No one would be able to see
that without a magnifying glass.
That is why useable maps done by proper cartographers nearly always
What has happened here is that this exagerration has gong too far
for zoom layer 16.
Merkaartor usese a hybrid approach
pixel_width_on_map = fixed_pixel_width + scale*estimated_real_width_in_m
On higher zoom levels, the second component dominates, on lower zoom
levels, the first component is the most important.
And even than, you cannot have one set of values that works for the
entire range of scales.
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