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Converting contour lines to polygons

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#1
Buzz

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I was hoping someone could help me with the following:

Learning about this tool prompted me to make this map for wikipedia. I made it by coloring the output of OMC and adding labels manually in Illustrator.

Since then, I've gathered some knowlegde on GIS and and I figured a similar result (for other countries) can be achieved by more time effiecient means. I've discovered that the VMAP0 dataset contains all the information I need, but I just can't seem to find a simple way of turning the contour lines contained in VMAP into the 'contour polygons' (similar to what you see in my illustrator map).

What I tried and sort of works:
* turning the elevation data in VMAP (contour lines and spot heights) into a TIN, and displaying the TIN in categories. Great results, but quite time consuming.

* Displaying DEM data (etopo30) in categories. Great results, but no vector output.

My question: is there an easy way of turning contour lines (or other elevation data) into polygons that can be filled in?

#2
Hans van der Maarel

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My question: is there an easy way of turning contour lines (or other elevation data) into polygons that can be filled in?

<{POST_SNAPBACK}>


If you can get them into Illustrator, you can do the following:
- Place a rectangle around them so you don't have any loose ends
- Select the contour lines and the rectangle and use the Split tool on the Pathfinder pallette (bottom row, leftmost one iirc)
- Ungroup everything
- You now have areas that you can fill in using the standard Illustrator way.

Hope this helps.
Hans van der Maarel - Cartotalk Editor
Red Geographics
Email: hans@redgeographics.com / Twitter: @redgeographics

#3
Martin Gamache

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Manifold has the option of creating courtour areas from a DEM rather than lines.

I'm not sure why you wouldn't just use a a hypsometric color image from a DEM though? I can't image that file size would be enough of a justification?

#4
Buzz

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Thanks for your replies.

@Hans van der Maarel

Great idea, although not quite what I was looking for. This would have definately worked better than the method I used, but what i would realy like is a softwaretool that does all this for me.

@Alpine mapping guild
The option in Manifold sounds pretty much like what I'm looking for, although I would prefer using the contourlines contained in the VMAP0 data as input rather than a DEM. Do you know if this is possible as well?

I've since also figured out how to make a vectorized, categorized height map from a DEM with a trial version of arcmap. But since the full Arcgis package is not exactly free, I now have a new question:

Do you know of any open source or free to use software that is capable of turning a DEM or other elevation data (like a set of contour lines) into a vectorized, colorized hypsometric map?

#5
Martin Gamache

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I think Microdem can do that, and other software such as SAGA...this has been discussed previously if you search the board.

but you did not answer my question as to why you want to use a vector version for the hyspo, sounds like extra work. Why not just use a screen resolutionDEM created image.

#6
Buzz

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but you did not answer my question as to why you want to use a vector version for the hyspo, sounds like extra work. Why not just use a screen resolutionDEM created image.


In order to minimize aliasing, I prefer to work with vectors. I think the increase in quality (especially visible at low resolutions) is worth the extra work.

I'll have a look at Microdem and Saga. Thanks for the tip.

#7
Buzz

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Thank you for your comments.

I see your point. In the case of hypsometric maps with a continuous color range and at a scale similar to or smaller than that of my Spain map (which is indeed typical of the future 'end products' I had in mind) , I agree that a raster would suffice. Also, I've abandoned the idea of using the contour lines contained in the DCW data, using SRTM data is indeed a much better option. However, I'm not convinced that aliasing will not be an issue if I were to use discrete color bands. I'll make some samples of both raster and vectorized hypsometric maps to compare and I'll post the results of the comparison.

#8
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I'll make some samples of both raster and vectorized hypsometric maps to compare and I'll post the results of the comparison.

<{POST_SNAPBACK}>



I will too!

#9
mdsumner

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The option in Manifold sounds pretty much like what I'm looking for, although I would prefer using the contourlines contained in the VMAP0 data as input rather than a DEM. Do you know if this is possible as well?


You can created "Bounded Areas" using the Transform Toolbar - but you'll have to close off the lines - using the drawing tools, or Join Lines, and maybe some topology problems etc. - for incompletely bounded regions, and you'll have to be careful with the Transfer Rules to correctly copy the attributes. It's possible it will all work in one or two steps, depending on the data.

There's was some detailed discussion about achieving this in Manifold a few years ago, I'd have to (re-)try an example to point out exactly what transfer rules work.




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