readshapefile returns a multipolygon as several polygons

Start at the Basemap.readshapefile entry point and reproduce the supplied Fiona example, comparing returned records with the source geometries. Done when the MultiPolygon case preserves one source feature's geometry and metadata without breaking the separate Polygon case.

I wanted to draw a choropleth map using basemap. My plan was to read the polygons from the shapefile vis readshapefile and then further process them using shapely, descartes, etc.

The problem that I encountered was that readshapefile returned multiple polygons for each MultiPolygon. This causes confusion, as for the enclosed polygon we will have more than one record.

I think the fix will be to return a MultiPolygon instead of multiple polygons.

Here is an example:

from collections import OrderedDict
import fiona
from mpl_toolkits.basemap import Basemap


rec1 = dict()
rec2 = dict()

rec1['id'] = 0
rec1['type'] = 'Feature'
rec1['properties'] = OrderedDict([(u'NAME', 'outer'),(u'VALUE', 100)])
rec1['geometry'] = dict()
rec1['geometry']['type'] = 'MultiPolygon'
rec1['geometry']['coordinates'] = [[[(-50,40),(50,40),
                                    (50,-40),(-50,-40),
                                    (-50,40)
                                   ]],
                                  [[(-45,35),(45,35),
                                    (45,-35),(-45,-35),
                                    (-45,35)
                                   ]]]

rec2['id'] = 1
rec2['type'] = 'Feature'
rec2['properties'] = OrderedDict([(u'NAME', 'inner'),(u'VALUE', 1)])
rec2['geometry'] = dict()
rec2['geometry']['type'] = 'Polygon'
rec2['geometry']['coordinates'] = [[(-45,35),(45,35),
                                    (45,-35),(-45,-35),
                                    (-45,35)
                                   ]]
driver = 'ESRI Shapefile'
crs = {'no_defs': True, 'ellps': 'WGS84', 'datum': 'WGS84', 'proj': 'longlat'}
schema = {'geometry': 'Polygon',
         'properties': {'NAME': 'str',
                'VALUE': 'float:15.2'}}

with fiona.open(
     '/tmp/foo.shp',
     'w',
     driver=driver,
     crs=crs,
     schema=schema) as c:
    c.write(rec1)
    c.write(rec2)

m = Basemap()
m.readshapefile('/tmp/foo','foo')
for info,region  in zip(m.foo_info, m.foo):
    print info
    print region

for which the output is:

{'RINGNUM': 1, 'NAME': 'outer', 'VALUE': 100.0, 'SHAPENUM': 1}
[(-50.0, 40.0), (50.0, 40.0), (50.0, -40.0), (-50.0, -40.0), (-50.0, 40.0)]
{'RINGNUM': 2, 'NAME': 'outer', 'VALUE': 100.0, 'SHAPENUM': 1}
[(-45.0, 35.0), (-45.0, -35.0), (45.0, -35.0), (45.0, 35.0), (-45.0, 35.0)]
{'RINGNUM': 1, 'NAME': 'inner', 'VALUE': 1.0, 'SHAPENUM': 2}
[(-45.0, 35.0), (45.0, 35.0), (45.0, -35.0), (-45.0, -35.0), (-45.0, 35.0)]