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Is there any tool available which let's me run millions of parcel shapefiles and simplify them?

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    what do you mean by simplify, the edge?
    – artwork21
    May 12, 2011 at 1:48
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    I think I would be concerned about running simplify on polygons without some type of topology. I don't even think esri will manage two edges being simpplified simultaneously so they remain consistent. Maybe I'm wrong.
    – Brad Nesom
    May 12, 2011 at 4:21

7 Answers 7

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Version 9.0 of GDAL/OGR added the -simplify option to the ogr2ogr command. The documentation indicates that it preserves topology.

-simplify tolerance: (starting with GDAL 1.9.0) distance tolerance for simplification. This method will preserve topology, in particular for polygon geometries.

Example usage:

ogr2ogr outfile.shp infile.shp -simplify 0.000001
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If your data is stored in PostGIS, try using ST_SimplifyPreserveTopology.

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You could try Shapely - a Python API built on top of GEOS. As both Shapely and GDAL have Python libraries you can easily combine them to data from many different sources (including shapefiles) and then simplifying and exporting as desired.

The only downside may be speed if you are doing millions of features - it could be faster to use GEOS or JTS directly.

See the simplify method:

All points in the simplified object will be within the tolerance distance of the original geometry. By default a slower algorithm is used that preserves topology. If preserve topology is set to False the much quicker Douglas-Peucker algorithm is used.

>>> p = Point(0.0, 0.0)
>>> x = p.buffer(1.0)
>>> x.area
3.1365484905459389
>>> s = x.simplify(0.05, preserve_topology=False)
>>> s.area
3.0614674589207187
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ogr2ogr has a "segmentize" option that appears to do what you need: GDAL ogr2ogr documentation

From that page:

-segmentize max_dist: (starting with GDAL 1.6.0) maximum distance between 2 nodes. Used to create intermediate pointsspatial query extents

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You could try Mapshaper. There are maybe some limitations due to your file size.

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GRASS v.generalize

http://grass.osgeo.org/gdp/html_grass64/v.generalize.html

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  • I made some test and as of today, all methods suggested here and relying on GEOS (ogr2ogr with -simplify, shapely, PostGIS's ST_SimplifyPreserveTopology function) produce topological anomalies (i.e. holes/overlaps between polygons). Only with GRASS I had good results.
    – capooti
    Sep 18, 2012 at 15:42
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Inspire from Mapshaper, but directly in local, look on https://github.com/migurski/Bloch

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  • thanks for your response. I guess the issue here is what to do if no topology is define with the shapefile
    – NetConstructor.com
    Jun 26, 2012 at 14:48

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