LayerMapping 是一个数据导入实用程序Link to this heading#LayerMapping 类提供了一种将矢量空间数据文件（例如 shapefile）的内容映射到 GeoDjango 模型的方法。
这个实用程序是为了消除重复的代码，用于从矢量图层中提取几何和字段，将其转换为另一个坐标系统（例如 WGS84），然后插入到 GeoDjango 模型中而产生的。
\n\n\n您需要一个受 GDAL 支持的数据源，比如一个 shapefile（这里我们使用一个简单的多边形 shapefile，名为 test_poly.shp，包含三个要素）：
>>> from django.contrib.gis.gdal import DataSource\n>>> ds = DataSource("test_poly.shp")\n>>> layer = ds[0]\n>>> print(layer.fields) # Exploring the fields in the layer, we only want the 'str' field.\n['float', 'int', 'str']\n>>> print(len(layer)) # getting the number of features in the layer (should be 3)\n3\n>>> print(layer.geom_type) # Should be 'Polygon'\nPolygon\n>>> print(layer.srs) # WGS84 in WKT\nGEOGCS["GCS_WGS_1984",\n DATUM["WGS_1984",\n SPHEROID["WGS_1984",6378137,298.257223563]],\n PRIMEM["Greenwich",0],\n UNIT["Degree",0.017453292519943295]]\n现在我们定义相应的 Django 模型（确保使用 migrate）：
from django.contrib.gis.db import models\n\n\nclass TestGeo(models.Model):\n name = models.CharField(max_length=25) # corresponds to the 'str' field\n poly = models.PolygonField(srid=4269) # we want our model in a different SRID\n\n def __str__(self):\n return "Name: %s" % self.name\n使用 LayerMapping 提取所有要素并将它们放入数据库中：
>>> from django.contrib.gis.utils import LayerMapping\n>>> from geoapp.models import TestGeo\n>>> mapping = {\n... "name": "str", # The 'name' model field maps to the 'str' layer field.\n... "poly": "POLYGON", # For geometry fields use OGC name.\n... } # The mapping is a dictionary\n>>> lm = LayerMapping(TestGeo, "test_poly.shp", mapping)\n>>> lm.save(verbose=True) # Save the layermap, imports the data.\nSaved: Name: 1\nSaved: Name: 2\nSaved: Name: 3\nHere, LayerMapping transformed the three geometries from the shapefile\nin their original spatial reference system (WGS84) to the spatial reference\nsystem of the GeoDjango model (NAD83). If no spatial reference system is\ndefined for the layer, use the source_srs keyword with a\nSpatialReference object to specify one.
LayerMapping APILink to this heading#以下是在实例化 LayerMapping 对象期间可以使用的参数和关键字：
参数 | \n描述 | \n
|---|---|
| \n地理模型，不是 实例 | \n
| \nThe path to the OGR-supported data source file\n(e.g., a shapefile). Also accepts\n | \n
| \n一个字典：键是与模型字段对应的字符串，值对应于 OGR 要素的字符串字段名称，或者如果模型字段是地理字段，则应该对应于 OGR 几何类型，例如 | \n
关键字参数 | \n\n |
|---|---|
| \n要使用的数据源中的图层的索引（默认为0）。 | \n
| \nUse this to specify the source SRS manually (for\nexample, some shapefiles don't come with a | \n
| \nSpecifies the character set encoding of the strings\nin the OGR data source. For example, | \n
| \n可以是 | \n
| \nSetting this to False will disable coordinate\ntransformations. In other words, geometries will\nbe inserted into the database unmodified from their\noriginal state in the data source. | \n
| \nSetting this to the name, or a tuple of names,\nfrom the given model will create models unique\nonly to the given name(s). Geometries from\neach feature will be added into the collection\nassociated with the unique model. Forces\nthe transaction mode to be | \n
| \n在导入空间数据时设置要使用的数据库。默认为 | \n
save() 关键字参数Link to this heading#The save() method also accepts keywords. These keywords are\nused for controlling output logging, error handling, and for importing\nspecific feature ranges.
保存关键字参数 | \n描述 | \n
|---|---|
| \nMay be set with a slice or tuple of\n(begin, end) feature ID's to map from\nthe data source. In other words, this\nkeyword enables the user to selectively\nimport a subset range of features in the\ngeographic data source. | \n
| \nWhen this keyword is set, status information\nwill be printed giving the number of features\nprocessed and successfully saved. By default,\nprogress information will be printed every 1000\nfeatures processed, however, this default may\nbe overridden by setting this keyword with an\ninteger for the desired interval. | \n
| \n默认情况下，非致命错误通知将打印到 | \n
| \n如果设置为整数，事务将在每个步骤间隔之后发生。例如，如果 | \n
| \nStatus information will be written to this file\nhandle. Defaults to using | \n
| \nExecution of the model mapping will cease upon\nthe first error encountered. The default value\n( | \n
| \n如果设置，将在执行数据库上的每个模型保存后打印信息。 | \n
As noted in the warning at the top of this section, Django stores all SQL\nqueries when DEBUG=True. Set DEBUG=False in your settings, and this\nshould stop excessive memory use when running LayerMapping scripts.
max_allowed_packet 错误Link to this heading#如果在使用 LayerMapping 和 MySQL 时遇到以下错误：
OperationalError: (1153, "Got a packet bigger than 'max_allowed_packet' bytes")\nThen the solution is to increase the value of the max_allowed_packet\nsetting in your MySQL configuration. For example, the default value may\nbe something low like one megabyte -- the setting may be modified in MySQL's\nconfiguration file (my.cnf) in the [mysqld] section:
max_allowed_packet = 10M\n