Exporting raster bitmap from shape file

gistfile1.py

RASTERIZE_COLOR_FIELD = "__color__"
RASTERIZE_COLOR = (158, 18, 110, 200)


pixel_size = 0.05

# Open the data source
orig_data_source = ogr.Open(args[0])

# Make a copy of the layer's data source because we'll need to 
# modify its attributes table
source_ds = ogr.GetDriverByName("Memory").CopyDataSource(orig_data_source, "")
source_layer = source_ds.GetLayer(0)
source_srs = source_layer.GetSpatialRef()
x_min, x_max, y_min, y_max = source_layer.GetExtent()

# Create the destination data source
x_res = int((x_max - x_min) / pixel_size)
y_res = int((y_max - y_min) / pixel_size)

# Create a field in the source layer to hold the features colors
field_def = ogr.FieldDefn(RASTERIZE_COLOR_FIELD, ogr.OFTInteger)
source_layer.CreateField(field_def)
source_layer_def = source_layer.GetLayerDefn()
field_index = source_layer_def.GetFieldIndex(RASTERIZE_COLOR_FIELD)

# Generate random values for the color field (it's here that the value
# of the attribute should be used, but you get the idea)
for feature in source_layer:
    feature.SetField(field_index, 158)
    source_layer.SetFeature(feature)

# Create the destination data source
x_res = int((x_max - x_min) / pixel_size)
y_res = int((y_max - y_min) / pixel_size)

target_ds = gdal.GetDriverByName('GTiff').Create(args[1], x_res, y_res, 4, gdal.GDT_Byte)

target_ds.SetGeoTransform((
        x_min, pixel_size, 0,
        y_max, 0, -pixel_size,
    ))

if source_srs:
    # Make the target raster have the same projection as the source
    target_ds.SetProjection(source_srs.ExportToWkt())
else:
    # Source has no projection (needs GDAL >= 1.7.0 to work)
    target_ds.SetProjection('LOCAL_CS["arbitrary"]')

# Rasterize
err = gdal.RasterizeLayer(
    target_ds, 
    (4, 3, 2, 1), 
    source_layer, 
    burn_values=(0, 0, 0, 0),
    options=["ATTRIBUTE=%s" % RASTERIZE_COLOR_FIELD]
)

if err != 0:
    raise Exception("error rasterizing layer: %s" % err)