[OSM-talk] displayed width of roads

Steve Chilton S.L.Chilton at mdx.ac.uk
Mon Feb 18 11:51:38 GMT 2008


snip:
> 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
--------------------------------------------------------------------

Robin

That is a very naïve view of the ability of any map (unless at a scale of exactly 1:1) to show the real world in anything like it's correct geo-locations and at correct scale. All mapping is a compromise to some degree or other. Features are exaggerated according to their importance in the scheme of things. This is particularly true of roads, which are by their nature are often stacked up in close proximity to other roads, cycleways, footways, bridges, buildings, boundaries, etc.

For some background - a quick Google search came up with the following, which is a piece on the Land Registry and the problems it has in interpreting features represented at various scales on the excellent Ordnance Survey maps.
http://www.boundary-problems.co.uk/mapaccuracy.htm

Having said that I do agree that at some of the mid-zooms in the mapnik layer the motorways are tending to coalesce at present. I will find time soon to have a look at experimenting with adjusting the widths (possibly seperating motorway_link out to separate (and thinner) styles - which they aren't at the moment). But eventually the way forward is some intelligence to allow the local and specific exaggeration/generalisation that would be done in "traditional cartography" where it is necessary.

Cheers
STEVE

Steve Chilton, Learning Support Fellow
Learning and Technical Support Unit Manager
School of Health and Social Sciences
Middlesex University
phone/fax: 020 8411 5355
email: steve8 at mdx.ac.uk
http://www.mdx.ac.uk/schools/hssc/staff/profiles/technical/chiltons.asp

Chair of the Society of Cartographers: http://www.soc.org.uk/

SoC conference 2008:
http://www.abdn.ac.uk/cartographers08/

-----Original Message-----
From: talk-bounces at openstreetmap.org [mailto:talk-bounces at openstreetmap.org] On Behalf Of Robin Paulson
Sent: 18 February 2008 10:16
To: talk at openstreetmap.org
Subject: Re: [OSM-talk] displayed width of roads

On 18/02/2008, Abigail Brady <morwen at evilmagic.org> wrote:
> > line is probably twice the width of the actual road. this causes
> > problems at even simple motorway junctions, as the whole thing becomes
> > a big blue mess. could i request this be looked into?
> >
>
> Well, if this isn't done, then roads quickly become hairlines at lower
> zooms.  There's not really much to look into. If you want to see the roads
> they have to be wider than they really are.

yes, they will. but i was talking about close-in zoom - the example i
gave was at zoom 16.  they don't have to be wider at that level, maybe
at zoom 4 they do, but i wouldn't care about details like this at that
zoom level anyway

as i understand it, the tiles are rendered separately for each zoom
level, so what we see at one zoom level is different to what we see at
another


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