---
title: "GeoDjango modell-API"
version: 6.0
locale: sv
source: https://docs.djangoproject.com/sv/6.0/ref/contrib/gis/model-api/
canonical: https://djangodocs.dev/sv/6.0/ref/contrib/gis/model-api/
---
# GeoDjango modell-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()
```

## Spatiala fälttyper

Spatiala fält består av en serie geometriska fälttyper och en rasterfälttyp. Var och en av geometrifälttyperna motsvarar OpenGIS Simple Features-specifikationen [^1]. Det finns ingen sådan standard för rasterdata.

### `GeometryField`

#### `class GeometryField`

Basklass för geometriska fält.

### `PointField`

#### `class PointField`

Lagrar en [`Point`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.Point).

### `LineStringField`

#### `class LineStringField`

Lagrar en [`LineString`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.LineString).

### `PolygonField`

#### `class PolygonField`

Lagrar en [`Polygon`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.Polygon).

### `MultiPointField`

#### `class MultiPointField`

Lagrar en [`MultiPoint`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.MultiPoint).

### `MultiLineStringField`

#### `class MultiLineStringField`

Lagrar en [`MultiLineString`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.MultiLineString).

### `MultiPolygonField`

#### `class MultiPolygonField`

Lagrar en [`MultiPolygon`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.MultiPolygon).

### `GeometryCollectionField`

#### `class GeometryCollectionField`

Lagrar en [`GeometryCollection`](/sv/6.0/ref/contrib/gis/geos/#django.contrib.gis.geos.GeometryCollection).

### `RasterField`

#### `class RasterField`

Lagrar en [`GDALRaster`](/sv/6.0/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALRaster).

`RasterField` är för närvarande endast implementerat för PostGIS backend.

## Alternativ för rumslig fältindelning

Förutom de vanliga [Alternativ för fält](/sv/6.0/ref/models/fields/#common-model-field-options) som finns tillgängliga för Django-modellfält, har spatiala fält följande ytterligare alternativ. Alla är valfria.

### `srid`

#### `BaseSpatialField.srid`

Ställer in SRID [^2] (Spatial Reference System Identity) för geometrifältet till det angivna värdet. Standardvärdet är 4326 (även känt som [WGS84](https://en.wikipedia.org/wiki/WGS84), enheterna är i grader av longitud och latitud).

#### Välja en SRID

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**
>
> Om du vill utföra godtyckliga avståndsfrågor med hjälp av icke-punktgeometrier i WGS84 i PostGIS och du vill ha anständig prestanda, aktivera nyckelordet [`GeometryField.geography`](#django.contrib.gis.db.models.GeometryField.geography) så att [geography database type](#geography-type) används istället.

Mer om detta:

- [spatialreference.org](https://spatialreference.org/): En Django-driven databas med rumsliga referenssystem.
- [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.

### `rumsligt_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.

## Alternativ för geometrifält

Det finns ytterligare alternativ tillgängliga för Geometry-fält. Alla följande alternativ är valfria.

### `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**
>
> För närvarande är 3D-stödet begränsat till PostGIS- och SpatiaLite-backends.

### `geografi`

#### `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**
>
> Geografistödet är begränsat till PostGIS och tvingar SRID att vara 4326.

### `max_geom_collections`

#### `GeometryField.max_geom_collections`

> **New in Django 5.2.17**

This option is forwarded to the [`form field`](/sv/6.0/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`.

#### Geography-typ

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).

Eftersom geografiska beräkningar kräver mer matematik är endast en delmängd av PostGIS rumsliga uppslagsord tillgängliga för den geografiska typen. I praktiken innebär detta att utöver [distance lookups](/sv/6.0/ref/contrib/gis/geoquerysets/#distance-lookups) är endast följande ytterligare [spatial lookups](/sv/6.0/ref/contrib/gis/geoquerysets/#spatial-lookups) tillgängliga för geografiska kolumner:

- [`bboverlaps`](/sv/6.0/ref/contrib/gis/geoquerysets/#std-fieldlookup-bboverlaps)
- `täckt av`
- `täcken`
- [`intersects`](/sv/6.0/ref/contrib/gis/geoquerysets/#std-fieldlookup-intersects)

Om du behöver använda en spatial lookup eller aggregat som inte stöder geografin som indata kan du använda databasfunktionen [`Cast`](/sv/6.0/ref/models/database-functions/#django.db.models.functions.Cast) för att konvertera geografikolumnen till en geometrityp i frågan:

```
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).

**Fotnoter**

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

[^2]: *Se id.* i kap. 2.3.8, s. 39 (Geometrivärden och rumsliga referenssystem).

[^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 och Hugh H. Howard, *Thematic Cartography and Geographic Visualization* (Prentice Hall, 2:a upplagan), kapitel 7.1.3.

[^5]: Denna begränsning gäller inte för PostGIS.

[^6]: Mer information finns i dokumentationen [PostGIS Geography Type](https://postgis.net/docs/using_postgis_dbmanagement.html#PostGIS_Geography).