Interpreting the B10 map for a DEM

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Interpreting the B10 map for a DEM

Postby Wangalade » Sun Feb 11, 2018 1:14 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.
Image
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

Postby Morfie » Mon Feb 12, 2018 5:20 am

DEM = Digital Elevation Model?
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Re: Interpreting the B10 map for a DEM

Postby Morfie » Mon Feb 12, 2018 5:30 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

Postby Mike » Mon Feb 12, 2018 7:13 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

Postby Big Mac » Mon Feb 12, 2018 9:28 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

Postby Cthulhudrew » Tue Feb 13, 2018 3:13 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

Postby Wangalade » Sat Feb 17, 2018 6:41 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/rationale-behind-methodology-of-my_6.html
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Re: Interpreting the B10 map for a DEM

Postby Big Mac » Sun Feb 18, 2018 10:57 am

Wangalade wrote:
Big Mac wrote:Have you got the link to your blog post, please

https://42ducktape.blogspot.com/2018/02/rationale-behind-methodology-of-my_6.html


Thankyou.
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Re: Interpreting the B10 map for a DEM

Postby Mike » Mon Feb 19, 2018 12:18 am

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

Postby Wangalade » Tue Feb 20, 2018 2:36 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

Postby Wangalade » Tue Feb 20, 2018 5:30 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.
Image
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