---
title: "GeoDjango モデル API"
version: 6.1
locale: ja
source: https://docs.djangoproject.com/ja/6.1/ref/contrib/gis/model-api/
canonical: https://djangodocs.dev/ja/6.1/ref/contrib/gis/model-api/
---
# GeoDjango モデル API

This document explores the details of the GeoDjango Model API. Throughout this
section, we'll be using the following geographic model of a [ZIP code](https://en.wikipedia.org/wiki/ZIP_code) and
of a [Digital Elevation Model](https://en.wikipedia.org/wiki/Digital_elevation_model) as our examples:

```
from django.contrib.gis.db import models

class Zipcode(models.Model):
    code = models.CharField(max_length=5)
    poly = models.PolygonField()

class Elevation(models.Model):
    name = models.CharField(max_length=100)
    rast = models.RasterField()
```

## 空間フィールドのタイプ

空間フィールドは一連のジオメトリフィールド型と1つのラスターフィールド型で構成されます。各ジオメトリフィールド型は OpenGIS Simple Features 仕様  [^1] に対応しています。ラスターデータに対するこのような標準は存在しません。

### `GeometryField`

#### `class GeometryField`

ジオメトリフィールドの基本クラス。

### `PointField`

#### `class PointField`

[`Point`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.Point) を格納します。

### `LineStringField`

#### `class LineStringField`

[`LineString`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.LineString) を格納します。

### `PolygonField`

#### `class PolygonField`

[`Polygon`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.Polygon) を格納します。

### `MultiPointField`

#### `class MultiPointField`

[`MultiPoint`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.MultiPoint) を格納します。

### `MultiLineStringField`

#### `class MultiLineStringField`

[`MultiLineString`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.MultiLineString) を格納します。

### `MultiPolygonField`

#### `class MultiPolygonField`

[`MultiPolygon`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.MultiPolygon) を格納します。

### `GeometryCollectionField`

#### `class GeometryCollectionField`

[`GeometryCollection`](/ja/6.1/ref/contrib/gis/geos/#django.contrib.gis.geos.GeometryCollection) を格納します。

### `RasterField`

#### `class RasterField`

[`GDALRaster`](/ja/6.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALRaster) を格納します。

`RasterField` は現在、PostGIS バックエンドのみで実装されています。

## 空間フィールドのオプション

Django のモデルフィールドで利用できる通常の [フィールドオプション](/ja/6.1/ref/models/fields/#common-model-field-options) に加えて、空間フィールドには以下の追加オプションがあります。すべてオプションです。

### `srid`

#### `BaseSpatialField.srid`

ジオメトリフィールドの SRID [^2] (Spatial Reference System Identity) を指定した値に設定します。デフォルトは 4326 (別名 [WGS84](https://en.wikipedia.org/wiki/WGS84) 、単位は緯度経度)。

#### SRID の選択

Choosing an appropriate SRID for your model is an important decision that the
developer should consider carefully. The SRID is an integer specifier that
corresponds to the projection system that will be used to interpret the data in
the spatial database. [^3]  Projection systems give the context to the
coordinates that specify a location. Although the details of [geodesy](https://en.wikipedia.org/wiki/Geodesy) are
beyond the scope of this documentation, the general problem is that the earth
is spherical and representations of the earth (e.g., paper maps, web maps) are
not.

Most people are familiar with using latitude and longitude to reference a
location on the earth's surface. However, latitude and longitude are angles,
not distances. In other words, while the shortest path between two points on a
flat surface is a straight line, the shortest path between two points on a
curved surface (such as the earth) is an *arc* of a [great circle](https://en.wikipedia.org/wiki/Great_circle).
[^4]

Thus, additional computation is required to obtain distances in planar units
(e.g., kilometers and miles). Using a geographic coordinate system may
introduce complications for the developer later on. For example, SpatiaLite
does not have the capability to perform distance calculations between
geometries using geographic coordinate systems, e.g. constructing a query to
find all points within 5 miles of a county boundary stored as WGS84. [^5]

Portions of the earth's surface may projected onto a two-dimensional, or
Cartesian, plane. Projected coordinate systems are especially convenient for
region-specific applications, e.g., if you know that your database will only
cover geometries in [North Kansas](https://spatialreference.org/ref/epsg/2796/), then you may consider using projection
system specific to that region. Moreover, projected coordinate systems are
defined in Cartesian units (such as meters or feet), easing distance
calculations.

> **Note**
>
> PostGISでWGS84の点以外のジオメトリを使用して任意の距離クエリを実行したい場合で、適切なパフォーマンスが必要な場合は、 [`GeometryField.geography`](#django.contrib.gis.db.models.GeometryField.geography) キーワードを有効にして、代わりに [ジオグラフィデータベース型](#geography-type) が使用されるようにします。

追加のリソース:

- [spatialreference.org](https://spatialreference.org/): A database of spatial reference systems.
- [The State Plane Coordinate System](https://web.archive.org/web/20080302095452/http://welcome.warnercnr.colostate.edu/class_info/nr502/lg3/datums_coordinates/spcs.html): A website covering the various
  projection systems used in the United States. Much of the U.S. spatial
  data encountered will be in one of these coordinate systems rather than
  in a geographic coordinate system such as WGS84.

### `spatial_index`

#### `BaseSpatialField.spatial_index`

Defaults to `True`. Creates a spatial index for the given geometry
field.

> **Note**
>
> This is different from the `db_index` field option because spatial
> indexes are created in a different manner than regular database
> indexes. Specifically, spatial indexes are typically created using
> a variant of the R-Tree, while regular database indexes typically
> use B-Trees.

## ジオメトリフィールドのオプション

ジオメトリフィールドには追加オプションがあります。以下のすべてのオプションは任意です。

### `dim`

#### `GeometryField.dim`

This option may be used for customizing the coordinate dimension of the
geometry field. By default, it is set to 2, for representing two-dimensional
geometries. For spatial backends that support it, it may be set to 3 for
three-dimensional support.

> **Note**
>
> 現時点では、3Dサポートは PostGIS と SpatiaLite バックエンドに限られています。

### `geography`

#### `GeometryField.geography`

If set to `True`, this option will create a database column of
type geography, rather than geometry. Please refer to the
[geography type](#geography-type) section below for more
details.

> **Note**
>
> ジオグラフィのサポートは PostGIS に限定され、SRID が 4326 に強制されます。

### `max_geom_collections`

#### `GeometryField.max_geom_collections`

> **New in Django 5.2.17**

This option is forwarded to the [`form field`](/ja/6.1/ref/contrib/gis/forms-api/#django.contrib.gis.forms.Field.max_geom_collections) generated for this model
field, bounding how many geometry collections may be contained in submitted
WKB/WKT inputs before raising [`ValueError`](https://docs.python.org/3/library/exceptions.html#ValueError). Since spatial field
assignments are lazy, it is also checked when values are accessed, e.g. when
saving an instance, but not when read from a database. It defaults to `198`.

#### ジオグラフィ (Geography) 型

The geography type provides native support for spatial features represented
with geographic coordinates (e.g., WGS84 longitude/latitude). [^6]
Unlike the plane used by a geometry type, the geography type uses a spherical
representation of its data. Distance and measurement operations
performed on a geography column automatically employ great circle arc
calculations and return linear units. In other words, when `ST_Distance`
is called on two geographies, a value in meters is returned (as opposed
to degrees if called on a geometry column in WGS84).

地理計算にはより多くの数学が関わるため、地理型に対して使用できる PostGIS 空間ルックアップのサブセットが限られています。具体的には、[距離ルックアップ](/ja/6.1/ref/contrib/gis/geoquerysets/#distance-lookups) に加えて、ジオグラフィカラム用に利用可能な追加の [空間ルックアップ](/ja/6.1/ref/contrib/gis/geoquerysets/#spatial-lookups) は以下のみです。

- [`bboverlaps`](/ja/6.1/ref/contrib/gis/geoquerysets/#std-fieldlookup-bboverlaps)
- [`coveredby`](/ja/6.1/ref/contrib/gis/geoquerysets/#std-fieldlookup-coveredby)
- [`covers`](/ja/6.1/ref/contrib/gis/geoquerysets/#std-fieldlookup-covers)
- [`intersects`](/ja/6.1/ref/contrib/gis/geoquerysets/#std-fieldlookup-intersects)

入力としてジオグラフィ型をサポートしていない空間ルックアップや集計を使用する必要がある場合、 [`Cast`](/ja/6.1/ref/models/database-functions/#django.db.models.functions.Cast) データベース関数を使用して、クエリの中でジオグラフィカラムをジオメトリ型に変換できます:

```
from django.contrib.gis.db.models import PointField
from django.db.models.functions import Cast

Zipcode.objects.annotate(geom=Cast("geography_field", PointField())).filter(
    geom__within=poly
)
```

For more information, the PostGIS documentation contains a helpful section on
determining [when to use geography data type over geometry data type](https://postgis.net/docs/using_postgis_dbmanagement.html#PostGIS_GeographyVSGeometry).

**脚注**

[^1]: OpenGIS Consortium, Inc., [Simple Feature Specification For SQL](https://www.ogc.org/standard/sfs/).

[^2]: *See id.* at Ch. 2.3.8, p. 39 (Geometry Values and Spatial Reference Systems).

[^3]: Typically, SRID integer corresponds to an EPSG ([European Petroleum Survey Group](https://epsg.org/)) identifier. However, it may also be associated with custom projections defined in spatial database's spatial reference systems table.

[^4]: Terry A. Slocum, Robert B. McMaster, Fritz C. Kessler, & Hugh H. Howard, *Thematic Cartography and Geographic Visualization* (Prentice Hall, 2nd edition), at Ch. 7.1.3.

[^5]: この制限は PostGIS には適用されません。

[^6]: 詳細は [PostGIS Geography Type](https://postgis.net/docs/using_postgis_dbmanagement.html#PostGIS_Geography) のドキュメントを参照してください。