[Tagging] Map a divide?

[Kevin Kenny]

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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Re: [Tagging] Map a divide?

[Tobias Zwick]

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 :
>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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Re: [Tagging] Map a divide?

[Warin]

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 
  tagged as
fixme=More accurate/better representation/make relation
fuzzy=5
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 

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   
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 :

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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Re: [Tagging] Map a divide?

[Kevin Kenny]

On Thu, Oct 4, 2018 at 6:26 PM Warin <61sundow...@gmail.com> wrote:
>
> A land form ridge too me is a 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'.

That divide is, ipso facto, a ridge line, because water flows downhill
- it is a line that's higher than the basins on either side. It runs
from peak to saddle to peak to saddle (admittedly, the 'peaks' may be
of but little prominence) for the length of the divide.

In any case, the place where I mean to map the divide is terrain of
considerable complexity, topographically. Its high point is the most
topographically prominent feature between Vermont and West Virginia.
The divide unquestionably runs for the most part along high ridges.
The 'ridge' nature gets lost only at a handful of saddles that are in
relatively high-elevation wetlands - but those flat lands are still
some hundreds of metres above the valley floors of the two rivers
whose basins it divides. The complexity comes from the fact that the
place is not a mountain range geologically. It is a 'dissected
plateau', whose 'peaks' are actually arêtes between chasms excavated
by glacial action. The direction of glacial flow was not consistent
among the glacial epochs, so the ridges tend to run higgledy-piggledy,
and one reason for mapping the divide is that it is otherwise tricky
to follow visually. It wanders quite a lot.

I live among some of the oldest exposed rock on the planet -
surrounding me are sediments from the early Palæozoic, and to the
north is the Canadian Shield, with its oldest rock dating to the
Hadean Æon, with its oldest samples having an estimated formation of
4.2 × 10⁹ years ago. Consequently, the mountains here are all rounded
and eroded. The ridges, except for the cols at the boundaries of
glacial cirques, are therefore broader and flatter-topped than you
appear to imagine - but they still rise distinctly above the
surrounding valleys.

Can we agree that https://www.flickr.com/photos/ke9tv/9514469053,
https://www.flickr.com/photos/ke9tv/9764660284,
https://www.flickr.com/photos/ke9tv/10031459724 and
https://www.flickr.com/photos/ke9tv/14799708048 are all indeed views
of a ridge? (In the last photo, ignore the mountains on the horizon,
they're in a different range - the ridge runs diagonally away from the
right foreground).

Or check out the contour lines (elevations in feet; my users are
American) along the Devil's Path
http://kbk.is-a-geek.net/catskills/test4.html?la=42.1294&lo=-74.1438&z=13
and tell me that I'm not dealing with a ridge!

Open question - which I'll resolve for myself - is how much
topographic prominence to use when labeling peaks and saddles.  I
think I'll probably follow the local hiking clubs, and say, '150 feet
(about 45 m) of prominence, and 1 km separation' for mapping peaks and
their key cols, and at this point I care about the key cols mostly so
as to keep the topology of the divide continuous - although I'll
surely map the names of the saddles where I know them! (They do have
local names, even though they aren't listed in GNIS or appear on very
many maps. But the locals could tell you where to find Mink Hollow,
Stony Clove, Lockwood Gap, Winisook Pass or Pecoy Notch - and yes, we
use all those words in toponyms, reflecting the Babel of languages
that our settlers spoke.)

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Re: [Tagging] Map a divide?

[Warin]

On 05/10/18 09:45, Kevin Kenny wrote:

On Thu, Oct 4, 2018 at 6:26 PM Warin <61sundow...@gmail.com> wrote:

A land form ridge too me is a 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'.

That divide is, ipso facto, a ridge line, because water flows downhill
- it is a line that's higher than the basins on either side. It runs
from peak to saddle to peak to saddle (admittedly, the 'peaks' may be
of but little prominence) for the length of the divide.

In any case, the place where I mean to map the divide is terrain of
considerable complexity, topographically. Its high point is the most
topographically prominent feature between Vermont and West Virginia.
The divide unquestionably runs for the most part along high ridges.
The 'ridge' nature gets lost only at a handful of saddles that are in
relatively high-elevation wetlands - but those flat lands are still
some hundreds of metres above the valley floors of the two rivers
whose basins it divides. The complexity comes from the fact that the
place is not a mountain range geologically. It is a 'dissected
plateau', whose 'peaks' are actually arêtes between chasms excavated
by glacial action. The direction of glacial flow was not consistent
among the glacial epochs, so the ridges tend to run higgledy-piggledy,
and one reason for mapping the divide is that it is otherwise tricky
to follow visually. It wanders quite a lot.

I live among some of the oldest exposed rock on the planet -
surrounding me are sediments from the early Palæozoic, and to the
north is the Canadian Shield, with its oldest rock dating to the
Hadean Æon, with its oldest samples having an estimated formation of
4.2 × 10⁹ years ago. Consequently, the mountains here are all rounded
and eroded. The ridges, except for the cols at the boundaries of
glacial cirques, are therefore broader and flatter-topped than you
appear to imagine - but they still rise distinctly above the
surrounding valleys.

Can we agree that https://www.flickr.com/photos/ke9tv/9514469053,
https://www.flickr.com/photos/ke9tv/9764660284,
https://www.flickr.com/photos/ke9tv/10031459724 and
https://www.flickr.com/photos/ke9tv/14799708048 are all indeed views
of a ridge? (In the last photo, ignore the mountains on the horizon,
they're in a different range - the ridge runs diagonally away from the
right foreground).

Or check out the contour lines (elevations in feet; my users are
American) along the Devil's Path
http://kbk.is-a-geek.net/catskills/test4.html?la=42.1294&lo=-74.1438&z=13
and tell me that I'm not dealing with a ridge!


You may be dealing with a single ridge line.

Now tell me there is a single ridge line for the Australian Great Divide and 
I'd get you to an ophthalmologist.
Some of it is not very sharp, more flat, so not a ridge line.
There may be cliffs and ridge lines in that area .. but they do not mark the 
divide.
 



Open question - which I'll resolve for myself - is how much
topographic prominence to use when labeling peaks and saddles.  I
think I'll probably follow the local hiking clubs, and say, '150 feet
(about 45 m) of prominence, and 1 km separation' for mapping peaks and
their key cols, and at this point I care about the key cols mostly so
as to keep the topology of the divide continuous - although I'll
surely map the names of the saddles where I know them! (They do have
local names, even though they aren't listed in GNIS or appear on very
many maps. But the locals could tell you where to find Mink Hollow,
Stony Clove, Lockwood Gap, Winisook Pass or Pecoy Notch - and yes, we
use all those words in toponyms, reflecting the Babel of languages
that our settlers spoke.)

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Re: [Tagging] Map a divide?

[Joseph Eisenberg]

> I do agree that a true ridge line may not point uphill all the time, but 
> still be a single ridge.
>
> 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.
>
> Thank you for noticing this! I had just looked at the proposal page
yesterday and was wondering where the directional thing came from.
It will make my life much easier if I can draw a whole named ridge as one
way, instead of splitting it at each topographical saddle and peak!
In Northern California, many named ridges are long, but are considered one
feature.

> Am 4. Oktober 2018 16:46:19 MESZ schrieb Kevin Kenny 
>  :
>
> 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.
>
> Re: the original question, I've been thinking of this myself.

Besides natural=ridge, which is an approved feature, but meant for
individual ridges, there is also the proposed feature natural=mountain_range
I believe this is the appropriate tag for the line formed by the crest of
the Appalachian Mountains, or the Sierra Nevada and Cascade crests in the
USA.
It could either be used as a way that follows the line of each individual
ridge, or you could use a relation and add each of the ridges.

I think natural=divide could be appropriate for a clearly defined drainage
divide which is not a mountain range; eg a range of hills or a series of
low ridges?
But there's no proposal page or wiki page yet.

On the previous discussion, several people warned that we should not
attempt to map all divides between water drainage areas, because there are
some flat areas like plateaus or plains where the drainage is not clear,
even if you survey the area in person or check good satellite imagery. But
if there is a clear ridgeline, that should be verifiable. I'm not certain
of the situation in the Catskills.
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Re: [Tagging] Map a divide?

[Joseph Eisenberg]

That divide is, ipso facto, a ridge line, because water flows downhill
> - it is a line that's higher than the basins on either side. It runs
> from peak to saddle to peak to saddle (admittedly, the 'peaks' may be
> of but little prominence) for the length of the divide.
>

Agreed. But I'd keep natural=ridge for individual named ridges (which may
have a few named peaks and saddles along it's length)
And use natural=mountain_range for the much larger features which continue
several or many named ridges and peaks and saddles.
Or natural=divide


> Can we agree that https://www.flickr.com/photos/ke9tv/9514469053,
>
https://www.flickr.com/photos/ke9tv/9764660284,
> https://www.flickr.com/photos/ke9tv/10031459724 and
> https://www.flickr.com/photos/ke9tv/14799708048 are all indeed views
> of a ridge?
>

Yes, agreed. The page for natural=ridge shows a rather low, gentle hill as
an example of a ridge.

Open question - which I'll resolve for myself - is how much
> topographic prominence to use when labeling peaks and saddles.  I
> think I'll probably follow the local hiking clubs, and say, '150 feet
> (about 45 m) of prominence, and 1 km separation' for mapping peaks and
> their key cols, and at this point I care about the key cols mostly so
> as to keep the topology of the divide continuous - although I'll
> surely map the names of the saddles where I know them!
>

I'd map all named peaks that have any topographical prominence, but include
the prominence=* in meters.

For example, the most visually significant mountain peak in my hometown is
"Lower Devil's Peak";
It rises over 600m from the valley floor, but only has about 15 meters of
topographical prominence,
because it connects to a high ridge leading to "Middle Devil's Peak" and
"Upper Devil's Peak" (both more prominent).

If you know the topographical prominence it's really helpful to add, to
show that this is a minor sub-peak.

For myself, in the USA, I also more or less follow your idea, adding
unnamed peaks with over 50m prominence,
especially if they have an accurate spot elevation on the USGS maps, even
if they are unnammed.

(BTW, the proposal for "Prominence" is underway; please comment:
https://wiki.openstreetmap.org/wiki/Proposed_features/key:prominence)
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Re: [Tagging] mast / tower / communication_tower (again)

[Graeme Fitzpatrick]

On Tue, 2 Oct 2018 at 00:24, Martin Koppenhoefer 
wrote:

>
> Certainly, choosing "communication tower" for both types but under
> different keys wasn't  a solution that satisfies our requirements (reduce
> confusion and be easily applicable while allowing to distinguish what
> people want to distinguish).
>

I've been doing some checking & I think it could well be time to deprecate
the whole man_made=communications_tower tag

https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dcommunications_tower

There's supposedly ~3500 of them worldwide, with ~200 in Australia / NZ /
SE Asia http://overpass-turbo.eu/s/CwE

Over the last few days, I've looked at 50 odd of these 200, & not one is a
"communications_tower": "a huge tower for transmitting radio applications
like television, radio, mobile phone or officials radio. It is often made
from concrete and usually a far visible landmark." - & by a amazing twist,
the one tower that I know of in Australia that does meet the criteria,
Black Mountain Tower in Canberra https://www.blackmountaintower.com.au/,
*isn't* listed as one!

All of them I've looked at, are clearly, from aerial imagery, only a

   - man_made =tower
   
   - tower:type =
   communication
   


I don't know how many of the 3500 worldwide are actually
communications_towers bu that definition, but I'd guess not more than a
dozen or 2?

I'd like to suggest that we deprecate that tag, settle on the engineering
definition given to differentiate between masts & towers:

"In structural engineering, *mast* is a vertical structure, supported by
external guys and anchors.
This is the only existing definite feature that could be used to
differentiate masts and towers."

& start cleaning things up.

Your thoughts?

Thanks

Graeme
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Re: [Tagging] mast / tower / communication_tower (again)

[Joseph Eisenberg]

Sounds sensible to me. If JOSM and ID support man_made=tower +
tower:type=communication with a preset, it won't be any more work than
typing in a single tag.
Does this require a proposal process? How does something become officially
deprecated?

On Fri, Oct 5, 2018 at 2:59 PM Graeme Fitzpatrick 
wrote:

>
>
>
> On Tue, 2 Oct 2018 at 00:24, Martin Koppenhoefer 
> wrote:
>
>>
>> Certainly, choosing "communication tower" for both types but under
>> different keys wasn't  a solution that satisfies our requirements (reduce
>> confusion and be easily applicable while allowing to distinguish what
>> people want to distinguish).
>>
>
> I've been doing some checking & I think it could well be time to deprecate
> the whole man_made=communications_tower tag
>
> https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dcommunications_tower
>
> There's supposedly ~3500 of them worldwide, with ~200 in Australia / NZ /
> SE Asia http://overpass-turbo.eu/s/CwE
>
> Over the last few days, I've looked at 50 odd of these 200, & not one is a
> "communications_tower": "a huge tower for transmitting radio applications
> like television, radio, mobile phone or officials radio. It is often made
> from concrete and usually a far visible landmark." - & by a amazing twist,
> the one tower that I know of in Australia that does meet the criteria,
> Black Mountain Tower in Canberra https://www.blackmountaintower.com.au/,
> *isn't* listed as one!
>
> All of them I've looked at, are clearly, from aerial imagery, only a
>
>- man_made =tower
>
>- tower:type =
>communication
>
>
>
> I don't know how many of the 3500 worldwide are actually
> communications_towers bu that definition, but I'd guess not more than a
> dozen or 2?
>
> I'd like to suggest that we deprecate that tag, settle on the engineering
> definition given to differentiate between masts & towers:
>
> "In structural engineering, *mast* is a vertical structure, supported by
> external guys and anchors.
> This is the only existing definite feature that could be used to
> differentiate masts and towers."
>
> & start cleaning things up.
>
> Your thoughts?
>
> Thanks
>
> Graeme
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Re: [Tagging] mast / tower / communication_tower (again)

[Graeme Fitzpatrick]

On Fri, 5 Oct 2018 at 16:17, Joseph Eisenberg 
wrote:

> Sounds sensible to me. If JOSM and ID support man_made=tower +
> tower:type=communication with a preset, it won't be any more work than
> typing in a single tag.
>

Can confirm that it's preset in iD, as I've just mapped one (a mobile phone
tower) but don't know about JOSM (or anything else)?


> Does this require a proposal process? How does something become officially
> deprecated?
>

Yep, that's the other question!

Thanks

Graeme
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