Difference between revisions of "GeoJSON draft version 5"

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Revision as of 10:42, 24 May 2007

Overview

GeoJSON is a data-interchange format for a variety of geographic data structures. GeoJSON can be used to represent a geometry, a feature, a collection of geometries, or a collection of features. The geometry types supported in GeoJSON are Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, and Box. Features in GeoJSON are geometry objects with additional properties. A geometry collection represents a list of geometries and a feature collection represents a list of features.

A complete GeoJSON data structure is always an object (in JSON terms). In GeoJSON, an object consists of a collection of name/value pairs - also called members. For each member, the name is always a string. Member values are either a string, number, object, array or one of the literals: true, false, and null. An array consists of elements where each element is a value as described above. Note that while the term member generally refers to a name/value pair, GeoJSON does use the name "members" in geometry collections and feature collections.

Definitions

Specification

  1. GeoJSON always consists of a single object. This object (referred to as the GeoJSON object below) represents a geometry, feature, collection of geometries, or collection of features.
  2. The GeoJSON object may have any number of members (name/value pairs).
  3. The GeoJSON object must have a member with the name "type". This member's value is a string that determines the type of the GeoJSON object.
    1. The value of the type member must be one of: "Point", "MultiPoint", "LineString", "MultiLineString", "Polygon", "MultiPolygon", "Box", "GeometryCollection", "Feature", or "FeatureCollection"
    2. A geometry is a GeoJSON object where the type member's value is one of: "Point", "MultiPoint", "LineString", "MultiLineString", "Polygon", "MultiPolygon", or "Box".
      1. In addition to the type member, a GeoJSON object that represents a geometry (referred to as a geometry object below) must have a member with the name "coordinates". The value of the coordinates member is always an array (referred to as the coordinates array below). The structure for the elements in this array are determined by the type of geometry.
        1. For type "Point", each element in the coordinates array is a number representing the point coordinate in one dimension. The order of elements follows x, y, z order (or longitude, latitude, elevation for coordinates in decimal degrees).
        2. For type "MultiPoint", each element in the coordinates array is a coordinates array as described for type "Point".
        3. For type "LineString", each element in the coordinates array is a coordinates array as described for type "Point". The coordinates array for a LineString must have two or more elements. A LinearRing is a special case of type LineString where the first and last elements in the coordinates array are equivalent (they represent equivalent points). Though a LinearRing is not explicitly represented as a GeoJSON geometry type, it is referred to in the Polygon geometry type definition.
        4. For type "Polygon", each element in the coordinates array is a coordinates array as described for type "LineString". Furthermore, each LineString in the coordinates array must be a LinearRing. For Polygons with multiple LinearRings, the first must be the exterior ring and any others must be interior rings or holes.
        5. For type "MultiPolygon", each element in the coordinates array is a coordinates array as described for type Polygon.
        6. For type "Box", the coordinates array must two elements. Each element in the coordinates array is a coordinates array as described for type "Point". The first element in the array represents the minx, miny corner of the box, and the second point represents the maxx, maxy corner of the box.
    3. A GeoJSON object with type "GeometryCollection" represents a collection of geomety objects.
      1. An object of type "GeometryCollection" must have a member with the name "members". The value corresponding to "members" is an array. Each element in this array is a geometry object as defined above.
    4. A GeoJSON object with the type "Feature" represents a geometry with additional properties (referred to as a feature object below).
      1. A feature object must have a member with the name "geometry". The value of the geometry member is a geometry object as defined above (a GeoJSON object with type "Point", "MultiPoint", "LineString", "MultiLineString", "Polygon", "MultiPolygon", or "Box").
      2. A feature object must have a member with the name "properties". The value of the properties member is an object (any JSON object).
    5. A GeoJSON object with the type "FeatureCollection" represents a collection of feature objects.
      1. An object of type "FeatureCollection" must have a member with the name "members". The value corresponding to "members" is an array. Each element in the array is a feature object as defined above.
  4. A GeoJSON object may have an member with the name "crs". If a GeoJSON object has a member named "crs", it is assumed to represent the coordinate reference system of the included geometry or geometries. If a GeoJSON object does not have a member named "crs", it is assumed that the server and client have a mutual understanding about the coordinate reference system of the included geometries. Clients may assume that a GeoJSON data structure without a member named "crs" contains geometries in a Geographic projection, in the WGS84 datum, with units in decimal degrees.
    1. The value of a member named "crs" must be an object. This object must have at least two named members: "type" and "properties". The value of the member named "type" must be a string. The value of the member named "properties" must be an object. This specification defines no further requirements for the structure of these objects. Instead, a convention is offered.
      1. To use EPSG codes to describe coordinate reference system, the "crs" member should have the following structure: "crs": {"type": "EPSG", "properties": {"code": 4326}}
      2. Note that the use of EPSG codes does not change the meaning of the coordinate order for a GeoJSON data structure. All coordinates in GeoJSON are in x, y order (longitude, latitude). This is true regardless of the schema used to represent the coordinate reference system.

Examples

Each of the examples below represents a complete GeoJSON object. Note that unquoted whitespace is not significant in JSON. Whitespace is used in the examples to help illustrate the data structures - though it is not required.

Geometries

Point

{
   "type": "Point",
   "coordinates": [100.0, 0.0]
}

MultiPoint

{
   "type": "MultiPoint",
   "coordinates": [
       [100.0, 0.0], [101.0, 1.0]
   ]
}

LineString

{
   "type": "LineString",
   "coordinates": [
       [100.0, 0.0], [101.0, 1.0]
   ]
}

MultiLineString

{
   "type": "MultiLineString",
   "coordinates": [
       [
           [100.0, 0.0], [101.0, 1.0]
       ],
       [
           [102.0, 2.0], [103.0, 3.0]
       ]
   ]
}

Polygon

No holes

{
   "type": "Polygon",
   "coordinates": [
       [
           [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]
       ]
   ]
}

With holes

{
   "type": "Polygon",
   "coordinates": [
       [
           [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]
       ],
       [
           [100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2]
       ]
   ]
}

MultiPolygon

{
   "type": "MultiPolygon",
   "coordinates": [
       [
           [ [102.0, 2.0], [103.0, 2.0], [103.0, 3.0], [102.0, 3.0], [102.0, 2.0] ]
       ],
       [
           [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ],
           [ [100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2] ]
       ]
   ]
}

Box

{
   "type": "Box",
   "coordinates": [[100.0, 0.0], [101.0, 1.0]]
}

GeometryCollection

{
   "type": "GeometryCollection",
   "members": [
       {
           "type": "Point",
           "coordinates": [100.0, 0.0]
       },
       {
           "type": "LineString",
           "coordinates": [
               [101.0, 0.0], [102.0, 1.0]
           ]
       }
   ]
}

Feature

{
   "type": "Feature",
   "geometry": {
       "type": "LineString",
       "coordinates": [
           [100.0, 0.0], [101.0, 1.0]
       ]
   },
   "properties": {
       "prop0": "value0",
       "prop1": "value1"
   }
}

FeatureCollection

{
   "type": "FeatureCollection",
   "members": [
       {
           "type": "Feature",
           "id": "id0",
           "geometry": {
               "type": "LineString",
               "coordinates": [
                   [102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]
               ]
           },
           "properties": {
               "prop0": "value0",
               "prop1": "value1"
           }
       },
       {
           "type": "Feature",
           "id": "id1",
           "geometry": {
               "type": "Polygon",
               "coordinates": [
                   [
                       [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]
                   ]
               ]
           },
           "properties": {
               "prop0": "value0",
               "prop1": "value1"
           }
       }
   ]
}

Same feature collection, with a member named "crs" to represent the coordinate reference system.

{
   "type": "FeatureCollection",
   "crs": {
       "type": "EPSG",
       "properties": {"code": 4326}
   },
   "members": [
       {
           "type": "Feature",
           "id": "id0",
           "geometry": {
               "type": "LineString",
               "coordinates": [
                   [102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]
               ]
           },
           "properties": {
               "prop0": "value0",
               "prop1": "value1"
           }
       },
       {
           "type": "Feature",
           "id": "id1",
           "geometry": {
               "type": "Polygon",
               "coordinates": [
                   [
                       [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]
                   ]
               ]
           },
           "properties": {
               "prop0": "value0",
               "prop1": "value1"
           }
       }
   ]
}