LayerMapping data import utility¶

Example¶

1. You need a GDAL-supported data source, like a shapefile (here we’re using a simple polygon shapefile, test_poly.shp, with three features):

   >>> from django.contrib.gis.gdal import DataSource
   >>> ds = DataSource('test_poly.shp')
   >>> layer = ds[0]
   >>> print(layer.fields) # Exploring the fields in the layer, we only want the 'str' field.
   ['float', 'int', 'str']
   >>> print(len(layer)) # getting the number of features in the layer (should be 3)
   3
   >>> print(layer.geom_type) # Should be 'Polygon'
   Polygon
   >>> print(layer.srs) # WGS84 in WKT
   GEOGCS["GCS_WGS_1984",
       DATUM["WGS_1984",
           SPHEROID["WGS_1984",6378137,298.257223563]],
       PRIMEM["Greenwich",0],
       UNIT["Degree",0.017453292519943295]]
   

2. Now we define our corresponding Django model (make sure to use syncdb):

   from django.contrib.gis.db import models
   
   class TestGeo(models.Model):
       name = models.CharField(max_length=25) # corresponds to the 'str' field
       poly = models.PolygonField(srid=4269) # we want our model in a different SRID
       objects = models.GeoManager()
       def __unicode__(self):
           return 'Name: %s' % self.name
   

3. Use LayerMapping to extract all the features and place them in the database:

   >>> from django.contrib.gis.utils import LayerMapping
   >>> from geoapp.models import TestGeo
   >>> mapping = {'name' : 'str', # The 'name' model field maps to the 'str' layer field.
                  'poly' : 'POLYGON', # For geometry fields use OGC name.
                  } # The mapping is a dictionary
   >>> lm = LayerMapping(TestGeo, 'test_poly.shp', mapping)
   >>> lm.save(verbose=True) # Save the layermap, imports the data.
   Saved: Name: 1
   Saved: Name: 2
   Saved: Name: 3
   

Here, LayerMapping just transformed the three geometries from the shapefile in their original spatial reference system (WGS84) to the spatial reference system of the GeoDjango model (NAD83). If no spatial reference system is defined for the layer, use the source_srs keyword with a SpatialReference object to specify one.

LayerMapping API¶

class LayerMapping(model, data_source, mapping[, layer=0, source_srs=None, encoding=None, transaction_mode='commit_on_success', transform=True, unique=True, using='default'])¶

The following are the arguments and keywords that may be used during instantiation of LayerMapping objects.

Troubleshooting¶

OperationalError: (1153, "Got a packet bigger than 'max_allowed_packet' bytes")

max_allowed_packet = 10M