Shapely - convert polygons to lines?

Question

Given a shapefile with polygons, how do I convert the polygons to individual lines instead? I know how to do this in QGIS, but I'm looking for a Shapely function which does the same thing.

score 13 · Accepted Answer · edited Aug 10 '20 at 18:25

bugmenot123 is ok but I find easier use the boundary of the polygons. If you have a multipolygon or a polygon with holes the boundary returns a multilinestrig, if you have a polygon without holes the boundary returns a linestring.

Here is a simple example so you can see how it works:

import shapely
from shapely.geometry import MultiPolygon, Point
pol1 = MultiPolygon([Point(0, 0).buffer(2.0), Point(1, 1).buffer(2.0)])
pol2 = Point(7, 8).buffer(1.0)
pols = [pol1, pol2]
lines = []
for pol in pols:
    boundary = pol.boundary
    if boundary.type == 'MultiLineString':
        for line in boundary:
            lines.append(line)
    else:
        lines.append(boundary)
for line in lines:
    print line.wkt

score 2 · Answer 2 · answered Mar 27 '18 at 08:50

2

According to https://shapely.readthedocs.io/en/stable/manual.html#polygons:

You can get the outer ring of a Polygon via its exterior property.
You can get a list of the inner rings via its interior property.

According to https://shapely.readthedocs.io/en/stable/manual.html#collections-of-polygons:

For a MultiPolygon you can iterate over its Polygon members via iterating via in or list() or explicitely using its geoms property.

Collect all the rings and you have the lines.

answered Mar 27 '18 at 08:50

bugmenot123

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Tbh, I actually output the individual lines by getting the coordinates defining the polygons' vertices then creating LineStrings from consecutive coordinates. But your solution works as well. – absolutelydevastated Mar 27 '18 at 09:01
3

Please post your own solution then. – bugmenot123 Mar 27 '18 at 11:34

Shapely - convert polygons to lines?

2 Answers2

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