[Tagging] Highway property proposal "covered=yes"

Randy rwtnospam-newsgp at yahoo.com
Sat Oct 31 19:40:05 GMT 2009

Anthony wrote:

>I've been thinking about this, and I do support your proposal.
>However, renderers should take care of this even if it isn't tagged
>this way.

Agreed, so long as there is a decipherable method of otherwise tagging it. 
But, let me qualify that: "Agreed, in theory. However, I don't object to 
giving renders helpful hints, as long as the hints don't deny reality."

>If a highway and a building cross at the same layer, the
>building should be made partially transparent so the way can be seen
>to be covering it.  In my opinion, only if the way is at a layer less
>than zero should the lines be dashed.  Thus one can see from the map
>whether the way goes through the building or goes under it.
I don't have a big problem with this, although, I think that in most cases 
where the highway goes under the building, it can be tagged as a tunnel. I 
grant that there are exceptions.

Be it dashed lines or semitransparancy, I don't have a strong preference 
in the case of highways. In the case of pedestrian ways (sidewalks, 
footpaths, etc.), neither of these works very well. Semi-transparency to 
display a line rather than, for example a road with fill between the 
lines, will not give a very distinct difference. However, my dashed line 
suggestion won't work there, either, since, mapnik, at least, renders 
sidewalks, etc. as dotted red ways. Possibly a color change would be a 
reasonable differentiator, but using color change for important feature 
differentiation should be avoided, due to the challenges of color 
blindness. I'm willing to let the renderers solve the rendering problem, 
as long as a difference is rendered.

>To my mind tags like "covered" and "shaded" are more appropriately
>used by the routers than the renderers.  I don't have a problem with
>them, but the renderers should be able to render without them.
I'm not sure that setting "if the way and the structure are at the same 
level the way goes through the structure" as default is the best way to 
go. I don't disagree, I just need to think about it some more.

>I'm still not sure if my example should be tagged with "tunnel" or
>not.  To my mind something doesn't become a tunnel just because you
>build something over top of it.  According to the wiki, "The tunnel
>tag is used to map ways that runs through an underground passage."
>Emphasis mine.  Though people tend to not agree with me when I nitpick
>wiki definitions :).

I think "underground" is an unfortunate qualifier on tunnels, and I'd like 
to see it removed. First of all, it's inaccurate. Look at the online 
dictionaries. Nearly all of them qualify tunnel as a passage under or 
_through_ something. An example (I think in Miriam-Webster) is the passage 
through an arena which the players use to access the field (my 
paraphrase). Secondly, if adopted strictly, if forces the creation of a 
separate tag with identical functionality for the above ground case.


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