How to intelligently degrade or smooth GIS data (simplifying polygons)?

user_11596 0
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I have detailed US county maps, from the TIGER LINE data sets. How might I sample, smooth, or degrade the data so that I get straighter, more boxy, less "noisy" shapes to represent the geographical features -- in this case just county boundaries and state lines, but maybe also in the general case?

The sampling could happen at rendering time if that can be done efficiently, or a parallel data set could be generated and stored. I am using PostGIS, and the lines are multi-polylines generated by shp2pgsql -- but any solution where you take a squiggly line and reduce it to a smoother line of roughly the same significance to a human interpreter would be very useful.

postgis gis geometry algorithm
7 Answers

Answer by @unmounted is correct, but I would like to add one more suggestion.

Always use function ST_SimplifyPreserveTopology instead of ST_Simplify in PostGIS. Both use the same underlying algorithm (Douglas-Peucker), but the former avoids any simplifications which would result in invalid geometries. For example, ST_Simplify may result in geometry which intersects itself.

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