I have some simple polygons that I would like to convert to polylines using the sf package in R. I have found st_polygonize to convert polylines to polygons but I cannot but the reserve operation. Some documentation suggested that st_segmentize would work but I haven't found it useful.

  • Hang on, do you want polygon to polyline or polyline to polygon? Your title says one, your first line says the other, then you say polylines to polygons...
    – Spacedman
    Commented Sep 4, 2019 at 19:37
  • I made a mistake in the title. Thanks for your answer to my question in the text! It's much simpler than I thought. Commented Sep 4, 2019 at 19:44

1 Answer 1


To convert a simple polygon P (that defines an area) to a line L use:

L = st_cast(P,"LINESTRING")

eg using pl from example(st_polygon):

> st_polygon(pl)
POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))
> st_cast(st_polygon(pl),"LINESTRING")
LINESTRING (0 0, 1 0, 1 1, 0 1, 0 0)

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