[OSM-talk] Boundary rendering bug

Toby Murray toby.murray at gmail.com
Wed Feb 9 06:33:23 GMT 2011

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:

You can see this county border being rendered heading south into Colorado:

There is a county border just to the west going north into Wyoming
that is not rendered:


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