Properly mapping dry washes

For the alluvial fans, I haven’t tried mapping the larger bajadas yet, but I think one large, unnamed geological=alluvial_fan polygon is probably the most sensible way to map it. I suppose you could also add nodes if you wanted to name each one, or arbitrarily break them up just for ease of mapping. I did map a some of the alluvial fans that had somewhat more definition, again with surface=gravel, like the big one at the outlet of Furnace Creek (there really is very little plant life on this one, although there’s actually some development, namely two of the park hotels): Way: 1256468840 | OpenStreetMap.

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What can you say about the incline, when you compare those. Is this a reason to choose the one or the other.

I’m very late to this party (i found this discussion via willkmis’ changeset comments), but i just wanted to say that I think natural=wadi is a pretty good solution for the area features. Distinguishing between “dry streams” and “dry rivers” is unnecessary. And I think the linear features should definitely remain waterway=river/stream.

And a general comment/rant about NHD data, which someone mentioned earlier in this thread: it drives me nuts when I find that people have dumped ALL the streams from a watershed into OSM: Every tiny little gully, with irrelevant “reach codes” and streams split into 100 segments. I’ve done some NHD imports myself, but I try to only grab the named streams and other significant valleys. (Sadly, NHD does not include “Canyon” names, so I have to find those using USGS maps or GNIS points.)

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It’s taken a while, but I’ve put together a draft proposal for the natural=wadi tag based on this discussion.

https://wiki.openstreetmap.org/wiki/Proposal:Natural%3Dwadi

I would be very grateful if anyone from this thread would like to contribute to the proposal! If I didn’t manage to capture all the information from the discussion, please call that out or edit the proposal to include it!

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That is a very good first draft. Thank you!

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Looks good to me.

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Excellent draft, it does a good job of capturing the details without being too verbose. One suggestion if possible…alongside the photo examples include a sat image capture showing how the aerial view translates to the ground view. Most mappers will be using the sat image so this does a good job of connecting the two and why the distinction matters. Again, just a suggestion if it’s possible to help clarify.

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Yes, looks good, one suggestion I have: create a new paragraph “definition” in the text part and move the text from the template there, and put a oneliner in the definition field of the template. This is usually not more than a few words (it must not be complete, but should be very concise)

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There are a couple of aerial images in this thread that I didn’t include in the proposal because I wasn’t sure about license compatibility.

Is it OK to take screenshots from Bing and post them in the wiki?

I’d suggest taking this statement out: “typically more large scrub and small trees than the surrounding terrain” . I usually see the opposite, less scrub and trees in the wash.
For example:

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I guess that makes sense. There are a variety of expressions of wadis depending on the local ecosystems and geology. I did notice that some of the wadis in the Middle East appear very sandy. And some wadis in sub-Saharan Africa have very dense scrub.

There was even one I was hiking in Arizona that collects more water than the surrounding terrain and has very dense scrub.

It’s a different (related) topic, but if you called the terrain in the foreground sparse scrub, the terrain in the wadi dense scrub, and the hillside to the left bare rock with very sparse scrub, would we have appropriate tags in OSM to make all those distinctions?

Vegetation density depends on the most recent path of water through the wadi/wash area and how much flow there was. The most recent path may very well be scrubbed free of brush and trees by recent major flows. But smaller flows may not uproot plants and simply provide them more water than the surrounding slightly higher area.

I’d like to include this in the example rendering in the proposal, but I would need to confirm license compatibility with the wiki. What do you know about where the images came from?

If you find an old enough one presumably it would be out of copyright (assuming that AU copyright is similar to UK, and other issues would not apply)?

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Indeed! Some plants like the Catclaw Acacia have adapted to living in washes so that their seeds only germinate after a flash flood.

Those Topographic maps are available through Geoscience Australia. We do actually do have a waiver to use their CC-BY licensed datasets, as long as the dataset is mentioned on the contributors page

You can find individual maps to download here

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Thanks, Taya! @Kai_Johnson

I’ve had a busy day holidaying, so haven’t been able to reply!

As you said, we have a waiver for GA’s topo maps.

It possibly gets a little bit complicated as they appear to have changed their map legend?

https://d28rz98at9flks.cloudfront.net/102240/Map_reading_guide_v4.pdf is their “How to read a map” booklet & p8 shows a “sample legend”, which doesn’t include that dry waterway rendering.

However, if you look at one of their 1:50000 maps: ArcGIS Dashboards , they do.

The 1:50000 map that I copied that legend from (which isn’t currently listed as downloadable, & which I don’t have with me!) was Army-issue, produced in the late 1960s, but has the same blurb across the bottom as the rest of the 1:50000s do.

So, Kai, I’d say that yes, we would be able to use that rendering scheme, but if you have any doubts / concerns, drop them an e-mail.

Thanks @Thiskal and @Fizzie41 !

It turns out that not all of the 50K maps have the same rendering or legend, but I managed to find one with the mainly dry watercourse.

It’s interesting to note that the difference between their rendering for sand and dry watercourses is just the light blue outline. Otherwise the dot pattern and color are the same. I think we want renderings that more clearly distinguish between those types of features.

Thanks for all the input! I think the draft is in good enough shape that it could be formally proposed. Is there anything else that should be changed before we do that?

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The proposal has been made to the Forum: [RFC] Feature Proposal - Tag:natural=wadi

Would someone here be able to cross-post to the tagging e-mail list?

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