I downloaded administrative shapefiles from www.gadm.com/country (China). The Python (Basemap) code below tells me that there are 2365 polygons in it. However the .csv and .dbf files included with the shapefiles tell me that there are only 344 administrative divisions at this level (which corresponds to real geography).
Forgive my lack of experience with shapefiles, but what could explain this discrepancy? Is it possible that this would be caused by small islands being considered a different polygon? If so, are there specific techniques to get rid of them?
My worry is that this increases 8-fold the computation time of point-to-polygon spatial joints, since there are 8 times more polygons.
from mpl_toolkits.basemap import Basemapchina_shapefile="C:/Users/.../CHN_adm_shp/CHN_adm2"m = Basemap(projection='merc',llcrnrlat=15,urcrnrlat=55,llcrnrlon=70,urcrnrlon=140,lat_ts=20,resolution='c')m.readshapefile(china_shapefile, 'provinces', drawbounds=True)print len(m.provinces)
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Forgive my lack of experience with shapefiles, but what could explain this discrepancy? Is it possible that this would be caused by small islands being considered a different polygon? If so, are there specific techniques to get rid of them?
My worry is that this increases 8-fold the computation time of point-to-polygon spatial joints, since there are 8 times more polygons.
from mpl_toolkits.basemap import Basemapchina_shapefile="C:/Users/.../CHN_adm_shp/CHN_adm2"m = Basemap(projection='merc',llcrnrlat=15,urcrnrlat=55,llcrnrlon=70,urcrnrlon=140,lat_ts=20,resolution='c')m.readshapefile(china_shapefile, 'provinces', drawbounds=True)print len(m.provinces)
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