[Tagging] Map a divide?

Warin 61sundowner at gmail.com
Thu Oct 4 22:25:07 UTC 2018


A land form ridge too me isa long, narrow raised part of a high edge formed by hill/mountains and 
there associated bits. A land form of a dividing range or continental 
divide does not have to be narrow, The 'dividing line' marks the 
separate water flow from one side to the other and should be 'long'. So 
I don't think a divide/range is a ridge necessarily. In fact a divide 
could have several ridges as part of the divide. Some sample 
divides/ranges? Andes 7,000 km https://en.wikipedia.org/wiki/Andes Rocky 
Mountains 4,800 km https://en.wikipedia.org/wiki/Rocky_Mountains Great 
Dividing Range 3,500 km https://en.wikipedia.org/wiki/Great_Dividing_Range

The last exists in OSM as an area Way211234843 <https://www.openstreetmap.org/way/211234843>  tagged as
fixme=More accurate/better representation/make relation
fuzzy=50000
name=Great Dividing Range
name:cs=Velké předělové pohoří
name:de=Australisches Bergland
name:es=Gran Cordillera Divisoria
name:nl=Groot Australisch Scheidingsgebergte
natural=mountain_range
source=OpenCycleMap terrain rendering
source:name=local_knowledge
wikidata=Q192583 <https://www.wikidata.org/wiki/Q192583>

There are 87 natural=divide in the data base ...
no wiki page to say what it is, looks to be used by North America

Sample found: Relation1643366 <https://www.openstreetmap.org/relation/1643366>  tagged as
FIXME=continue
name=Sierra Crest
natural=divide
route=natural
type=route


----------------
I do agree that a true ridge line may not point uphill all the time, but still be a single ridge.

On 05/10/18 01:54, Tobias Zwick wrote:
> The definition in the wiki is a bit contradictory, in my opinion. On the one side, it states the thing about that the arrows should point away from the saddle point towards the peaks, like steps or a oneway street, on the other side it describes a ridge to connect several peaks and saddle points. Tagging the whole ridge as one way would be impossible if you followed that "arrow points upward" rule.
>
> There is also no mention of that rule in the original approved proposal. Looking at the history of the article, that rule was added in January 2018, following a short, well "discussion" about how a ridge could be rendered.
> The change made amounts to a incompatible, as your enquiry shows, redefinition of the ridge tag because one cannot anymore correctly tag a whole ridge as one way.
>
> We have two options to go from here:
> 1. Revert that definition change, continue to allow tagging ridges as one way  spanning over several peaks
> 2. Leave the wiki definition as it is currently and you tag "name=Catskill Divide" on every of the multiple natural=ridge ways you'd have to create along the whole way
>
> I'd favour the first option because
> 1. Redefinition of an existing tag is a no go
> 2. The reason why the definition was changed was to make it easier to render a ridge in a certain suggested way. Don't know if it is even rendered this way now (on osm-carto), but in any case this'd be tagging for the renderer, as the information where the ridge goes up and where it goes down is already present in the peak/saddle nodes
>
> Cheers
> Tobias
>
> Am 4. Oktober 2018 16:46:19 MESZ schrieb Kevin Kenny <kevin.b.kenny at gmail.com>:
>> In some maps that I render, I want to show the divide between a couple
>> of major river basins. (I have a good DEM for the area in question and
>> can derive the line readily.)
>>
>> In light of the recent thread on topographic prominence, I wonder if
>> this is sufficiently interesting information at least to push it to
>> OSM. (If not, that's fine, I have a PostGIS database and a bucket of
>> shapefiles and know what to do.)
>>
>> If it is sufficiently interesting, the question then arises: how to
>> map/tag it?
>>
>> 'natural=ridge' comes to mind, and the divide in question has a local
>> name. (The 'Catskill Divide' separates the basins of the Hudson and
>> Delaware Rivers.) This approach appears to run into problems, as I
>> read the Wiki. I see:
>>
>>> The way should connect saddle points and peaks, and the arrows should
>> point upwards.
>>
>> That may be all right for a ridge ascending the flank of a single
>> mountain, but what I'm talking about is the spine of a range, with the
>> ridge traversing dozens of named peaks. Even with a single mountain,
>> if there are false summits, the arrows on a single way cannot point
>> upward all the time! (And the wiki is clear that the
>>
>> Do I misread, and should the reading instead simply be that the
>> arrowhead should be higher than the arrow tail? In that case, I could
>> break the divide into two ways, with a common endpoint at the highest
>> summit in the range.
>>
>> Consider this a low-priority item. I have (or will have - there is a
>> bit of debugging yet) the data. I know how to render them. I'm happy
>> enough with a shapefile or a private PostGIS table if others aren't
>> interested.
>>
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