Extract points/coordinates from a polygon in Shapely

So, I discovered the trick is to use a combination of the Polygon class methods to achieve this.

If you want geodesic coordinates, you then need to transform these back to WGS84 (via pyproj, matplotlib's basemap, or something).

from shapely.geometry import Polygon#Create polygon from lists of pointsx = [list of x vals]y = [list of y vals]some_poly = Polygon(x,y)# Extract the point values that define the perimeter of the polygonx, y = some_poly.exterior.coords.xy

It took me a while to learn that a Polygon has an exterior boundary and possibly several interior boundaries. I am posting here because some of the answers don't reflect that distinction, though to be fair the original post did not use as an example a polygon with interior boundaries.

The points forming the exterior boundary are arranged in a CoordinateSequence, which can be obtained as

polygon.exterior.coords

You can find the length of this object using len(polygon.exterior.coords)and can index the object like a list. To get the first vertex, for example, use polygon.exterior.coords[0]. Note that the first and last points are the same; if you want a list consisting of the vertices without that repeated point, use polygon.exterior.coords[:-1].

You can convert the CoordinateSequence (including the repeated vertex) to a list of points thus:

list(polygon.exterior.coords)

Similarly, the CoordinateSequence consisting of the vertices forming the first interior boundary is obtained as polygon.interiors[0].coords, and the list of those vertices (without the repeated point) is obtained as polygon.interiors[0].coords[:-1].

You can use the shapely mapping function:

>>> from shapely.geometry import Polygon, mapping>>> sh_polygon = Polygon(((0,0), (1,1), (0,1)))>>> mapping(sh_polygon){'type': 'Polygon', 'coordinates': (((0.0, 0.0), (1.0, 1.0), (0.0, 1.0), (0.0, 0.0)),)}