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Line topology in Illy

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#1
David Medeiros

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When building maps in Illustrator (with or without MAPub) how do you handle topology when simplifying lines for features that are co incident in certain locations?

For example, you import a shapefile of the US state boundaries; each state is an individual polygon. Shared boarders between states are exactly the same, one on top of the other. When you simplify the polygons to reduce anchor points or change segmented lines to curves, you affect each polygon differently even with the same level of simplify… now your boundaries are no longer exactly matched and you have gaps and overlaps between them.

Is there a way to handle this process so that you can simplify co incident lines such that they will still match each other afterwards?

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#2
Hans van der Maarel

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The MAPublisher simplify command will retain line topology, so there shouldn't be any gaps.
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#3
David Medeiros

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The MAPublisher simplify command will retain line topology, so there shouldn't be any gaps.


Correct me if I'm wrong, but MAPub's simplify command does not create smooth curves, it retains the segmented lines right?

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#4
Hans van der Maarel

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The MAPublisher simplify command will retain line topology, so there shouldn't be any gaps.


Correct me if I'm wrong, but MAPub's simplify command does not create smooth curves, it retains the segmented lines right?


That is correct.

Another way to do it would be to take border lines, smooth those then use the Illustrator pathfinder tools to create areas out of them.
Hans van der Maarel - Cartotalk Editor
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#5
David Medeiros

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I wonder if using the MAPublisher simplify command first to get the desired amount of generalization, followed by a 99% Illustrator simplify to curve the segments would work. At most scales 99% doesn't show much change in line topology.

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#6
frax

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My workflow is ArcGIS > Illustartor (no MAPub). I usually have country borders as a separate layer in the GIS, that are not just the polygons. If you use polygons then you get two lines for each shared border. After simplifying things in Illy, the borders and the polygons don't necessarily match up, but you have to zoom in so far to see it, so I usually just ignore it.

For coastlines and land polygons that is usually one layer/shape in Arc, but I have them separate in Illy - I often want the coastlines to be higher in the layer order. I simplify the layer in Illy then duplicate - that way they match up.
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#7
MapMedia

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I simplify polygons and any dependent shapes in ArcMap using Generalize polygon/polyline.
I only simplify roads, rivers, railway, etc., in Illy.

#8
Hans van der Maarel

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I wonder if using the MAPublisher simplify command first to get the desired amount of generalization, followed by a 99% Illustrator simplify to curve the segments would work. At most scales 99% doesn't show much change in line topology.


Just tried this and it appears to work. That is, there's tiny overlaps and slivers after the Illustrator simplify but depending on your scale that might not be an issue.
Hans van der Maarel - Cartotalk Editor
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#9
David Medeiros

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I wonder if using the MAPublisher simplify command first to get the desired amount of generalization, followed by a 99% Illustrator simplify to curve the segments would work. At most scales 99% doesn't show much change in line topology.


Just tried this and it appears to work. That is, there's tiny overlaps and slivers after the Illustrator simplify but depending on your scale that might not be an issue.


Same here, I tried it yesterday on my watershed polygons and it works pretty well. I can now use thinner boundary lines since there are no gaps to hide beneath them and the lines themselves don't separate very much.

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