[Tagging] layer=-1, rivers, bridges and tunnels

Jaakko Helleranta.com jaakko at helleranta.com
Fri Mar 14 15:15:51 UTC 2014

Re; tagging a (complete or longer segment of a) river with layer=-1

I don't understand why anyone would do this. That's it. Why?

Layer= tag clearly (logically) implies that some data is above or below
some other data. At least to my logic. And I don't seem to be the only one
with this thinking. At least OsmAnd renders all waterways with layer=-1
with dashed casing, as if they were underground, which to me makes sense,
but what makes all rivers with this unnecessary tag render oddly. There are
quite a number of such problematic waterways (also) in Nicaragua and Haiti.

So, again : why tag things with with layer= tag when they are essentially
on ground level = not above or below other data (or at least natural
objects that might be mapped one day *) ? Am I missing something here?


*) I do add layer=1 to all bridges I map even if there wouldn't be any data
under then at the moment and think that this kind of layer tag use makes

Sent from my Android device. * +505-8845-3391 * http://about.me/jaakkoh
El mar 14, 2014 8:52 a.m., "Fernando Trebien" <fernando.trebien at gmail.com>

> Hello everyone,
> This is a small issue that came up recently in Brazil. In my
> understanding, the layer tag has no specific meaning other than to
> specify a rendering order. The wiki, however, states that it is wrong
> to tag a whole river with layer=-1. The reason for that, as far as I
> could figure, is because current validators (such as JOSM's or
> KeepRight's) will not issue a warning on a waterway x highway crossing
> when their layers are different, leading some users into tagging the
> river with layer=-1 in order to get rid of warnings about missing
> bridges and tunnels. So, I think that the validation rule is
> inadequate: it should warn when a waterway crosses a highway that has
> no bridge or tunnel tag, regardless of the value in the layer tag.
> (Fords are the only exception, AFAIK.)
> Do you agree that the river can be tagged with layer=-1 as long as
> this value is correct in relation to the layer of other
> nearby/crossing ways?
> --
> Fernando Trebien
> +55 (51) 9962-5409
> "The speed of computer chips doubles every 18 months." (Moore's law)
> "The speed of software halves every 18 months." (Gates' law)
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