Adding custom feature attributes to shapefile using OGR in Python

Question

I am seeking a way to take an existing Shapefile that has a Feature set of 200 countries. Each country Feature has an attribute of "NAME." My objective is to create a Python script that adds an arbitrary (for now) additional attribute, say, "POPULATION".

Of course I have the OSGeo and GeoDjango modules installed. I'm as far as:

 from osgeo import ogr
 infile = ogr.Open('sample.shp', 1) #'sample.shp' is a pre-existing ESRI shapefile described above
 inlyr = ogr.GetLayerByIndex(0)

Am I missing an OGR function that will allow me to insert Feature attribute fields into an existing Shapefile?

Answer 1

Is it possible to add a field to an existing shapefile using Python OGR..

from osgeo import ogr
driver = ogr.GetDriverByName('ESRI Shapefile')
dataSource = driver.Open("c:/test/Test2.shp", 1) #1 is read/write
#define floating point field named DistFld and 16-character string field named Name:
fldDef = ogr.FieldDefn('DistFld', ogr.OFTReal)
fldDef2 = ogr.FieldDefn('Name', ogr.OFTString)
fldDef2.SetWidth(16) #16 char string width
#get layer and add the 2 fields:
layer = dataSource.GetLayer()
layer.CreateField(fldDef)
layer.CreateField(fldDef2)

• Dave X: Thanks. To populate and write the data, I added these: for feat in layer: feat.SetField('Name','myname') layer.SetFeature(feat) dataSource=None

Answer 2

I believe the Assemble TIGER Polygons sample has what you're looking for:

# Open the datasource to operate on.
ds = ogr.Open( infile, update = 0 )
poly_layer = ds.GetLayerByName( 'Polygon' )
#############################################################################
# Create output file for the composed polygons.
nad83 = osr.SpatialReference()
nad83.SetFromUserInput('NAD83')
shp_driver = ogr.GetDriverByName( 'ESRI Shapefile' )
shp_driver.DeleteDataSource( outfile )
shp_ds = shp_driver.CreateDataSource( outfile )
shp_layer = shp_ds.CreateLayer( 'out', geom_type = ogr.wkbPolygon,
 srs = nad83 )
src_defn = poly_layer.GetLayerDefn()
poly_field_count = src_defn.GetFieldCount()
for fld_index in range(poly_field_count):
 src_fd = src_defn.GetFieldDefn( fld_index )
 fd = ogr.FieldDefn( src_fd.GetName(), src_fd.GetType() )
 fd.SetWidth( src_fd.GetWidth() )
 fd.SetPrecision( src_fd.GetPrecision() )
 shp_layer.CreateField( fd )

• mattdeboard: Thanks, is this just something you were familiar with beforehand or did you find it after searching?
• Derek Swingley: NP, I knew of the samples but looked through a few to find this specific piece.
• mattdeboard: Ah ok, great. I am going to wait until I'm at home and can try to implement this before I mark this as answered, but it's looking good.
• klewis: The example above creates a new shapefile. Then you must transfer all the other fields and geometry from existing to new file. Do you need an example that adds a field to an existing shapefile?
• Derek Swingley: @klewis- you might want to ask this as a question on the original question. I was notified of your response but I don't think the OP will be.