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Is it correct to tag a river with layer=-1 if it is not underground?

I have seen stretches of rivers tagged as such, even though they are not underground. I have always understood a negative value for layer to imply that something is underground. I thought this was documented on the wiki, but I cannot find any explicit mention under:


asked 08 Oct '12, 17:35

davespod's gravatar image

accept rate: 0%

I think you wanted Key:layer which mentions the issue.

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answered 08 Oct '12, 17:48

EdLoach's gravatar image

EdLoach ♦
accept rate: 22%


Much embarrassment - it is a while since I used the wiki, and had forgotten about the page naming conventions! Thanks!

(08 Oct '12, 19:15) davespod

I would add that mostly all non-underground rivers that have a negative layer tag on them indicate some kind of layering problems along the river. If you find a river tagged with layer=-1 and you can figure out what exactly is wrong with it then fix it.

(08 Oct '12, 19:29) RM87

There is nothing wrong with layer=-1 on an above-ground river. I can think of an example locally where there are multiple train tracks and roads crossing each other with a stream below them all. Rather then use high layer numbers on everything else the stream is layer=-1.

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answered 08 Oct '12, 19:41

pnorman's gravatar image

accept rate: 18%


That's a good example. Yet the wiki currently states "negative values [...] for features that are below ground" which I think is wrong. The layer key shouldn't say anything about below or above ground, just about the relative position to other objects.

(08 Oct '12, 21:10) scai ♦

The wiki has contained the words "below ground" or "underground" for around 18 months (incorrectly in my view, since "below ground" implies an absolute rather than relative value).

Voted-up answers here (and posts on the mailing lists) have consistently agreed with the "relative" interpretation. Whilst I suspect that that the wiki editor was trying to be helpful, I don't think that they succeeded.

(08 Oct '12, 23:48) SomeoneElse ♦

I know we should not tag for the renderers or for the validators, but there are situations where I have used the layer=-1 tag.

This was some time ago so maybe the validators have been upgraded to accommodate a stream crossing a path or vice versa at layer=0.

The crossing is neither a ford nor are there stepping-stones: No, the water trust trickles across the path. I have crossed a few places where the removal of boots is recommended.

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answered 10 Oct '12, 11:21

dcp's gravatar image

accept rate: 0%


From your description I would probably have used a shared node with no tags, rather than have one way crossing the other, although technically it sounds like you are "fording" the water so could mark it as a ford.

(10 Oct '12, 12:42) EdLoach ♦

I can follow your argument and you are right according to the Oxford dictionary: ford; noun; "Shallow place where river,etc. may be crossed by wading or in vehicle". Wikipedia defines it the same!

However, our renderers ignore the wading and show a automobile icon as a ford. Map features also defines it as a vehicle crossing ignoring the wading.

Next time I come across a wading ford I'll do as you suggest but add vehicle=no. Do you think that would be a good idea?

(10 Oct '12, 18:24) dcp

You don't need the vehicle tag if the path already forbids vehicles. But I agree that the current rendering is irritating.

(10 Oct '12, 19:15) scai ♦

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question asked: 08 Oct '12, 17:35

question was seen: 4,071 times

last updated: 10 Oct '12, 19:15

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum