[OSM-talk] Boundary rendering bug

Daniel Sabo danielsabo at gmail.com
Wed Feb 9 12:53:06 GMT 2011

This is probably a holdover from "old style" multipolygons that were defined by the tags on the outer ways and had no tags on the relations. But putting tags on both the way and the relation would be wrong anyways, because the renderer can't know that boundary on the way is the same boundary on the relation.

If your going to use boundary relations don't put any of the boundary tags on the member ways, let the importer apply them if the renderer needs it.

- Daniel

On Feb 8, 2011, at 10:33 PM, Toby Murray wrote:

> I think I have identified a Mapnik style bug in boundary rendering but
> since I am not very familiar with rendering rules I thought I would
> make sure other people think it is a bug before I submit a ticket
> about it.
> A few days ago I reworked the county boundaries in Colorado and then
> tonight in Wyoming.
> In Colorado I stripped all the tags off of the ways except for
> boundary=administrative and put them all into boundary relations.
> After this change, someone I know in Colorado complained that the
> county borders stopped rendering in osmarender. When I mentioned this
> on IRC it was suggested to leave admin_level=6 on the ways as well as
> in the relations. Kind of tagging for the renderer I suppose... but
> I've seen worse :)
> Anyway, I tried this in Wyoming tonight. Turns out this has an adverse
> effect on Mapnik rendering.
> Ways that only have boundary=administrative and are members of a
> boundary relation with admin_level=6 in the relation are rendered
> starting at z9. However if the way has admin_level=6 on it, while
> still being in an identical relation, then mapnik doesn't start
> rendering the boundary until z11.
> It strikes me as odd that a tag on a member way affects the rendering
> of a relation in this way. Am I missing something?
> You can see the effect here:
> http://www.openstreetmap.org/?lat=41.326&lon=-107.747&zoom=9&layers=M
> You can see this county border being rendered heading south into Colorado:
> http://www.openstreetmap.org/browse/way/98395444
> There is a county border just to the west going north into Wyoming
> that is not rendered:
> http://www.openstreetmap.org/browse/way/98838375
> Toby
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