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Generalizing jagged shorelines

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#1
sitesatlas

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I needed to generalize a number of the larger lakes from the SRTM Water Body Dataset (90m resolution) for use in small scale maps, but I didn't like the results of simply running Simplify or Normalize Topology with reduced precision in Manifold. However, I was able to get satisfactory results using a combination of buffers and inner buffers. I thought I'd share what I found to help other users who need to generalize shoreline or coastline data and to get feedback on how to improve the method.

To keep the water surface to a minimum:
Step 1, remove smallest inlets and islands: inner buffers 250m, invert selection, delete, delete non-contiguous areas, buffers 250m, invert selection, delete.
Step 2, smooth shorelines: buffers 1000m, invert selection, delete, inner buffers 1000m, invert selection, delete.
Step 3, simplify and smooth: simplify 500m, spline 5.

The distances above are somewhat arbitrary, so they'll need to be adapted to specific needs. Increase the distances above for more generalization, decrease them for less generalization.

To maximize the water surface instead, change step 1 to perform buffers first, then inner buffers, delete non-contiguous areas. Next, continue with steps 2 and 3.

I'm attaching a GIF of the end result of the first method, minimizing the water surface (black line) and the alternative method (white line), which maximizes it.

Does anyone have a different or better method?

Attached Files


Michael Borop
World Sites Atlas
http://www.sitesatlas.com

#2
eli

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I use MapShaper sometimes.

#3
sitesatlas

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I use MapShaper sometimes.


Thanks for the tip -- I'm going to try it out.
Michael Borop
World Sites Atlas
http://www.sitesatlas.com

#4
Fran├žois Goulet

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I use MapShaper sometimes.


I use MapShaper too, relatively often, and so far it works great for what I had to do. I mostly use the Modified V-W Simplification method...




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