How to create a polygon feature class from polylines in Python ArcGIS?

Question

I am trying to create a polygon from polylines. I've created this script but it gives errors of Arrays.

import arcpy
polyline=r'C:\temp\temp_lines.shp'
Output_polygon=r'C:\temp\temp_polygon.shp'
polygonArray = arcpy.Array()
polygonArray.add(polyline)
cursor = arcpy.InsertCursor(Output_polygon)
row = cursor.newRow()
polygon = arcpy.Polygon(polygonArray, "")
row.SHAPE = polygon
cursor.insertRow(row)
del row
del cursor

score 8 · Accepted Answer · edited Apr 13 '17 at 12:33

You need to break it down to points if they're good points and reconstruct. Polylines are made from paths, polygons are made from rings. Although they are created in a similar way they are not compatable, hence your error.

Go through each point on the line adding a point to your output array and then insert.

here's a post that might help Get all the points of a polyline

This should work, though it's only a fragment... you have to set your own FeatureClass and make an insert cursor to accept the polygon:

rows = arcpy.da.SearchCursor(FeatureClass)
desc = arcpy.Describe(FeatureClass)
shapefieldname = desc.ShapeFieldName

for row in rows:
    feat = row.getValue(shapefieldname) # input line
    PArray = arcpy.Array() # new polygon
    partnum = 0
    for part in feat:
        for pnt in feat.getPart(partnum):
            PArray.add(arcpy.Point(pnt.X,pnt.Y))
        # you will need to check that the first and last point are the same
        partnum += 1
    OutPoly = arcpy.Polygon(PArray) # now it's a polygon

Have a read of these:

Reading Geometries http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001t000000

Writing Geometries http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Writing_geometries/002z0000001v000000/

Thanks Michael. I tested the code and it gave this error: feat = row.getValue(InFc) # input line NameError: name 'row' is not defined — Mehdi, May 15 '14 at 06:54
Thanks a lot, Michael. I've got it working with some tweaks. — Mehdi, May 19 '14 at 09:09
I just tested this and it worked well for me. I populated a list with OutPoly and used that in an insert cursor to create my polygons feature class. Define a list before the loop, then at the end say OutPolyList.append(OutPoly). — jbalk, Oct 20 '16 at 04:50

How to create a polygon feature class from polylines in Python ArcGIS?

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