Interpreting the B10 map for a DEM

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Wangalade
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Interpreting the B10 map for a DEM

Post by Wangalade » Sun Feb 11, 2018 12:14 am

I already posted this on the Mystara Cartographic Society Facebook group, but I figure I should post it here too for maximum coverage.

As I mentioned in my blog post, I was never really satisfied with the DEM of karameikos. I'm not sure how I should interpret the map provided in B10. The first problem is determining the elevation of the base of the mountains. The mountain peaks average at 4500 ft, and the flatlands around kelven are about 1000 ft.
Image

The bigger problem is figuring out which lines are ridges or valleys. Are they a mix, or are they all valleys/ridges? In some areas, such as in the sierra nevadas (picture1), the valleys stand out more and form a more distinctive line. In others, like the alps (picture 2) the ridges are more defined. Of course there are some ranges where both the ridges and valleys stand out equally.
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Image

I think the big long lines are ridges of course and the little circle areas might be peaks, and I tend to think the branches are probably ridge. What are your opinions?
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Re: Interpreting the B10 map for a DEM

Post by Morfie » Mon Feb 12, 2018 4:20 am

DEM = Digital Elevation Model?

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Re: Interpreting the B10 map for a DEM

Post by Morfie » Mon Feb 12, 2018 4:30 am

From the map, the only valley is the white area marked the Lost Valley.
You could guess the lines between mountain ridges are valleys (such as the line to the right of K in PEAK) but there is no way of telling for sure.

The cloud area behind the label is also quite annoying..

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Re: Interpreting the B10 map for a DEM

Post by Mike » Mon Feb 12, 2018 6:13 pm

I don't think the "ridge lines" actually represent anything except "mountains are here". If they are ridges they make no togographical sense.

For example, northwest of the "lost valley" there are cross ridges without a central ridge. Does that mean there are a dozen mountain passes linking the lost valley with Darokin?

The next valley east from Threshold, if you follow it north, turns into a line that runs sideways (vertically) across the mountain range. If it is a ridge, it is disconnected from the rest of the mountain range, implying two north-south mountain passes, one on either side. Also the ridge ends abruptly at the edge of the mountains... a towering cliff? More likely it looks like the line represents the bottom of a canyon cutting through the mountain range Where is the river that dug this canyon? And in either case, why would the road to Selenica go up and over the mountains to the west, when it could take a water-level route through this enormous gap? (There is another of these vertical cross-ridges west of Threshold...)

The most damning evidence is in the upper right corner, where a river runs lengthwise along the side a mountain ridge, flowing over half a dozen cross-ridges. That is just ridiculous. Clearly there must be a valley it is flowing through, and a north-south ridge east of the valley. As such, the lines that are drawn here are either incorrect or merely indicative of "generic mountains" rather than actual topography.

My view is that this is artistic license, no more accurate than the hexagon symbols, and the apparent ridge lines are simply impressionistic hatching. I think you can infer some topography from the lines if you like, especially in the immediate environs of Threshold, but it is less accurate as you get further away, much of it has to be ignored as nonsensical.

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Re: Interpreting the B10 map for a DEM

Post by Big Mac » Mon Feb 12, 2018 8:28 pm

Wangalade wrote:I already posted this on the Mystara Cartographic Society Facebook group, but I figure I should post it here too for maximum coverage.

As I mentioned in my blog post, I was never really satisfied with the DEM of karameikos.
Have you got the link to your blog post, please. :)
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Re: Interpreting the B10 map for a DEM

Post by Cthulhudrew » Tue Feb 13, 2018 2:13 am

Mike wrote:My view is that this is artistic license, no more accurate than the hexagon symbols, and the apparent ridge lines are simply impressionistic hatching. I think you can infer some topography from the lines if you like, especially in the immediate environs of Threshold, but it is less accurate as you get further away, much of it has to be ignored as nonsensical.
I tend to agree. I think it was probably more to give the map some depth rather than any attempt to accurately define the ridgelines and slopes of those mountains (although certainly I think in some cases it could be interpreted that way).
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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Sat Feb 17, 2018 5:41 pm

Mike wrote: northwest of the "lost valley" there are cross ridges without a central ridge. Does that mean there are a dozen mountain passes linking the lost valley with Darokin?
that could be sloping up and then a sheer cliff face down, in either direction works I guess. As has been said, it's hard to know how to interpret it exactly. I don't have all the answers, I'm just trying to find a consistent methodology of interpretation so I can create data based on the maps provided.
Mike wrote:My view is that this is artistic license, no more accurate than the hexagon symbols, and the apparent ridge lines are simply impressionistic hatching. I think you can infer some topography from the lines if you like, especially in the immediate environs of Threshold, but it is less accurate as you get further away, much of it has to be ignored as nonsensical.
Yes, it is obvious whoever made the map was not a cartographer and more of an artist, but that doesn't mean I should discard the whole thing. I'm going to use as detailed data as I can get, but that means interpreting some geographically inaccurate maps to make them somewhat geographically sensible. The key to this is being consistent.

this is how I interpreted the map for my project
Image

but like I said I'm not happy with it; I don't like how the mountains plateau around the base, and I want to make the smaller ridges more pronounced. I just need to know which lines are ridges, etc.
Big Mac wrote:Have you got the link to your blog post, please
https://42ducktape.blogspot.com/2018/02 ... -my_6.html
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Re: Interpreting the B10 map for a DEM

Post by Big Mac » Sun Feb 18, 2018 9:57 am

Wangalade wrote:
Big Mac wrote:Have you got the link to your blog post, please
https://42ducktape.blogspot.com/2018/02 ... -my_6.html
Thankyou.
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Re: Interpreting the B10 map for a DEM

Post by Mike » Sun Feb 18, 2018 11:18 pm

Wow great article. You are approaching it the same way I am, taking the oldest material as the most canonical/accurate. Fun read, and interesting speculation on map projections. I downloaded the "rainfall patterns" article, it is very interesting.

On topic, you mentioned you are not happy with the elevation data and the plateauing. I interpret the hexmap "hill" and "mountain" symbols not as absolute elevation, but as local relief. If they were absolute elevation, then Atruaghin and Adri Varma should be wall to wall mountain tiles, not plains or whatever. I figure hills indicate a local relief of maybe 500-2000 feet, while mountains have a vertical relief of more than a couple thousand feet. If the local terrain has less than several hundred feet of elevation then it is plains or forest. But that could be lowland, plateau, a continuous slope cut with shallow gullies, or even a gentle hills. A hill or mountain could be a single butte, a ridge, a deep valley, or a wall-to-wall mountain range.

My approach for the Cruth Range would be to first locate the east-west watershed ridge line That will be a series of peaks connected by high saddle-ridges, and will generally mark the highest elevation peak. All rivers will flow away from this line, and all ridges will branch off from it. Next locate the known rivers. I tend to do draining first, not elevation, since water is what determines the landform. Every area should be drained by some river, so I fill in river channels between the known rivers until the entire area has a drainage network. The rivers should slope in elevation continuously from the watershed ridge to the level.

After that, I add ridges in between the rivers. The ridges should generally descend in elevation from the watershed line down to the level, though there will be some peaks; and toward the middle of the mountains some ridge peaks can even be higher than the watershed line. Finally I go back and add some variety: some passes and gaps, some canyons, some plateaus or lakes or bluffs, to add interest.

With regard to the B10 map, I'd use that as an impressionistic inspiration. Use the 6-mile hexmap to determine how much local relief there should be, and the B10 map to get an idea of ridges and valleys. But I'd start with the watershed ridge, and interpret the B10 map in a way that doesn't conflict with it. I'd also suggest that the Duke's Road Pass is one of the lowest passes in the range, and the rest of the ridge should he higher and more rugged. If there are other low passes they will be known and used by locals and monsters.

The narrow ridges around the lost valley make me think the valley is on a plateau surrounded by steep but low ridge-walls. Since the important village of Armstead is just north, there must be somethign about these walls that prevent local hunters from finding the hidden valley from the north. My thought is precipitous bluffs infested with predatory monsters, perhaps rocs or thunderheads or something. A short ridge which drops two thousand feet on the other side coudl explain the narrow-looking ridges between the lost valley and darokin. But a ridge several thousand feet high on both sides and only a mile wide is a knife-edge!

I don't know of a good computer tool to do this kind of work. I tend to either do it on paper, or write my own software. Such software as I have used makes it easy to add lumps but has little or no support for ridges.

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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Tue Feb 20, 2018 1:36 am

I'm going to reiterate my goals and methods. I'm trying to create an elevation model of Karameikos that stays as accurate to all the source material available for the area that is as geographically accurate as possible. Yes I generally place the older sources at a higher place of precedence, but in cases where a newer source provides more data and doesn't contradict the original source, then I will use the newer sources where possible. Map K from B10 is pretty faithful to the original 6mph map, the biggest discrepancies are in the path of the rivers. I have plans on how i'm going to redo the rest of Karameikos in making a DEM, but as I said it's just interpreting the way the mountains are drawn in Map K that is giving me issues. the series of north/south ridge/peaks and passes fits pretty well with how the hexes line up any way. If you notice on the hex map, the north western border are hills and not mountains, so that is one spot where the b10 map seems to contradict the hex map. That doesn't mean the steep mountains aren't there and the inaccessibility of the valley as stated in the module can't be true. If the majority of the hex are hills then the steep mountains can still be there. My point is that I'm am trying to adhere to all the sources, so if the map says there are ridges in a certain pattern I'm going to adhere to that as closely as possible.

To make a DEM requires a software package with interpolation tools. This can be found with most GIS software. I use either ArcGIS or QGIS, QGIS is open source and free for use. Depending on the interpolation method the DEM may have dimples or ridges or be smooth, it all depends on the data and the interpolation method.
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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Tue Feb 20, 2018 4:30 am

I wrote a blog post with what I am probably going to use as a method of interpretation for Map K.

In the map below I have marked what I consider to be the direction of slope in this interpretation. the red arrows point downslope, the red circles are peaks, and the yellow lines are low points or the bottom of a saddle.
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Re: Interpreting the B10 map for a DEM

Post by stanles » Sun Jan 27, 2019 11:48 pm

How are you progressing with this Wangalade?
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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Mon Jan 28, 2019 1:46 am

I haven't worked on this particular aspect of Karameikos for a while. I put it aside because there were some other things I wanted to approach before I worked on rebuilding the DEM.
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Re: Interpreting the B10 map for a DEM

Post by Tom Bulls Eye » Wed Feb 20, 2019 11:16 am

The map uses ridgeline/crestline representation. In short if you have two peaks, the crestline/ridgeline is the route which at all points between the two peaks will have the highest altitude. A peak is present at any point where at least three crestlines meet.

It is very useful for mountaineering since it presents a very easy way to represent and understand the layout of the crests, which is all you can spot from the bottom of the valley.

If you're scrambling in the mountains and you want to go from one peak to the next, following the crestline is usually the best route (theoretically also the shortest), but it doesn't provide you with information about the existence of a pass or height differences.

Generally, all mountains ranges have a central ridge, from which dependent ridges spread out. some towards the valleys in a herring bone fashion, others towards other central ridges. Two central ridges connected by crestlines indicate a massif. Central peaks can be located on the central ridges and also between two central ridges.

The problem with the map is, that the central crestlines all run in the wrong direction for this type of geological formation. It simply lacks the central crestline(s) going East-West, which confuses.

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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Wed Feb 20, 2019 5:46 pm

Tom, you seem to have some experience with this type of map, can you point me to some real world examples in the same style?

What are your opinions about the specifics on this map, where are peaks, massifs, etc?
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Re: Interpreting the B10 map for a DEM

Post by Tom Bulls Eye » Thu Feb 21, 2019 10:59 am

The easiest way to find it is to google ridge-line map or crest-line map. They are quite common.

The normal way to draw a crest-line representation is by determining the longest axis of the mountain range and start from the valley which is the closest to the first peak in the mountain range. Then you start connecting the valley to the first peak along points of highest altitude (crests/ridges), the first peak to the second peak, the second to the third and so on. Eventually you will reach the end of the mountain range or a valley without crests or ridges, and the crest-line ends at that point.

As you are following the long axis from peak to peak, all the highest peaks will by definition be found on the central crest-line.

The way geology and plate tectonics works, all central crest-lines will be perpendicular to the plate movement, i.e. following the longest axis of the mountain range.

This aspect is absent from the B10 map of Karameikos, which causes confusion and non-physical mountains (but magic could be a factor, who knows - no plate tectonics, raised solely by magic). The longest continuous lines in the B10 map are accordingly meant to be the the central ranges of the Crush Mountains/ Altan Tepes - range. but as mentioned they run the wrong way compared to convention.

Subsequently, you draw as many crest-lines connecting the lands outside the mountain range or the valleys in the mountain range to the central crest-line as necessary (i.e. each time you have a crest or ridge), and you obtain a crest-line map of the first central range within your mountain range. From the central crest-line, secondary crests-lines spread out, and these secondary crest-lines may themselves have connecting crest-lines which provides you with the outline of valleys and foothills.

When reading a crest-line map, it is important to remember that the crest-line represents a barrier! So two central crest-lines interconnected by secondary crest-lines indicates an impassible barrier, where you have to climb a number of ridges up and down into the intermediate valleys in order to cross this part of the mountain range. A structure like that is a massif.

As already mentioned, a peak is present wherever at least three crest-lines meet in a single point.

However, by making the assumption that the Crush Mountains and the Altan Tepes meet and slide on each other at the Lost Valley, then the map could be plausible from a geological point of view. This would create an elevated valley not unlike Valle Central of Costa Rica, where the Andes and the Rockies meet and slide off each other.

In that situation the crest lines of the two mountain ranges are correctly aligned with the Altan Tepes sliding south on the map and the Crush mountains sliding North.

Would make Threshold plagued by earthquakes though.

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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Thu Feb 21, 2019 5:46 pm

The only things that are coming up on Google are links or maps of specific places called crestline or Ridgeline, and sites talking about how to identify ridges on topographic maps.
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Re: Interpreting the B10 map for a DEM

Post by Tom Bulls Eye » Wed Feb 27, 2019 9:27 am

Odd, I get bad hits from google now as well. When I googled the topic originally, I was presented with a number of maps and also a book discussing why ridgeline representation had been abandonned in favor of topographic maps. Now I only get the hits you report as well.

That’s google for you. Emphasizing the modern and commercial aspects in their algorithms.

As I wrote in my first entry, ridgeline representation used to be the way to present maps before topographic maps became standard.

Imagine you are Captain Cook circumnavigating an island in Hawaii for the first time in your frigate. How will you map the heights from your ship during circumnavigation with just a sextant and trigonomic tables? You measure line of sight heights and distances to the peaks during travel and then connect the dots afterwards.

Thats how and why ridgeline representations used to be so common, because topographic mapping requires far more datapoints to be measured.

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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Wed Feb 27, 2019 3:59 pm

Not sure if this is what you're talking about, but I found Cartographic Relief Presentation by Eduard Imhof. He refers to these as edgelines in general and skeletal lines to refer to both ridges and drainage lines.

For how common you say this map type used to be, it's suprising I never ran across any during my years of education studying geography and cartography. At my University we had one of the most extensive map libraries in the country and I never came a map of this sort. Maybe they were there the whole time, but with how integral they seem to be to creating topographic maps, you would think they would at least be mentioned.
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Re: Interpreting the B10 map for a DEM

Post by Tom Bulls Eye » Wed Feb 27, 2019 6:39 pm

Seems we’re aligned now. I’m not a native speaker of English, so much may have been lost in translation.

I learned it as a boy scout in Denmark, it was one of the tasks in mapmaking to make these rudimentary maps with simple tools and compare our results with the topographic 4 cm: 1 km maps of the Danish Geodaetic Institute. Later my brother while studying navigation used them a lot. And, when scrambling in the mountains I’ve used these maps as well.

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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Wed Feb 27, 2019 7:47 pm

See when I was a boyscout we used the topographic quadrangle maps produced by the USGS. Though you can't get new ones in print anymore, they've started doing everything digitally. It was annoying in my geography field studies classes because no one knew how to read a topographic map or had any sense of direction at all.

I've messaged one of my professors who was involved in cartography before the digital age to see if he can provide me with any input about this.
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Re: Interpreting the B10 map for a DEM

Post by Wangalade » Thu May 16, 2019 7:34 am

after looking at more of geoff wingate's art, I went back and analyzed this map in more detail.

Peaks are peaks of actual mountains, saddles are simply different branches of the separate mountains running into each other, summits appear where ridges branch off from the main slope. I figured the only way to explain the northwest of the lost valley was to have the outer face be steep cliffs with the drawn ridges descended into the valley.

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