GeoJSON H. Butler
Internet-Draft Hobu Inc.
Intended status: Standards Track M. Daly
Expires: December 25, 2016 Cadcorp
A. Doyle
S. Gillies
Mapbox
S. Hagen
T. Schaub
Planet Labs
June 23, 2016
The GeoJSON Format
draft-ietf-geojson-04
Abstract
GeoJSON is a geospatial data interchange format based on JavaScript
Object Notation (JSON). It defines several types of JSON objects and
the manner in which they are combined to represent data about
geographic features, their properties, and their spatial extents.
GeoJSON uses a geographic coordinate reference system, World Geodetic
System 1984, and units of decimal degrees.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 25, 2016.
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.2. Conventions Used in This Document . . . . . . . . . . . . 4
1.3. Specification of GeoJSON . . . . . . . . . . . . . . . . 4
1.4. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
1.5. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. GeoJSON Text . . . . . . . . . . . . . . . . . . . . . . . . 7
3. GeoJSON Object . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Geometry Object . . . . . . . . . . . . . . . . . . . . . 7
3.1.1. Position . . . . . . . . . . . . . . . . . . . . . . 7
3.1.2. Point . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.3. MultiPoint . . . . . . . . . . . . . . . . . . . . . 9
3.1.4. LineString . . . . . . . . . . . . . . . . . . . . . 9
3.1.5. MultiLineString . . . . . . . . . . . . . . . . . . . 9
3.1.6. Polygon . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.7. MultiPolygon . . . . . . . . . . . . . . . . . . . . 10
3.1.8. Geometry Collection . . . . . . . . . . . . . . . . . 10
3.1.9. Antimeridian Cutting . . . . . . . . . . . . . . . . 10
3.1.10. Uncertainty and Precision . . . . . . . . . . . . . . 11
3.2. Feature Object . . . . . . . . . . . . . . . . . . . . . 11
3.3. Feature Collection Object . . . . . . . . . . . . . . . . 12
4. Coordinate Reference System . . . . . . . . . . . . . . . . . 12
5. Bounding Box . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. The Connecting Lines . . . . . . . . . . . . . . . . . . 14
5.2. The Antimeridian . . . . . . . . . . . . . . . . . . . . 14
5.3. The Poles . . . . . . . . . . . . . . . . . . . . . . . . 15
6. Extending GeoJSON . . . . . . . . . . . . . . . . . . . . . . 15
6.1. Foreign Members . . . . . . . . . . . . . . . . . . . . . 15
7. GeoJSON Types are not Extensible . . . . . . . . . . . . . . 16
7.1. Semantics of GeoJSON Members and Types are not Changeable 16
8. Versioning . . . . . . . . . . . . . . . . . . . . . . . . . 17
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9. Mapping 'geo' URIs . . . . . . . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. Interoperability Considerations . . . . . . . . . . . . . . . 18
11.1. I-JSON . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.2. Coordinate Precision . . . . . . . . . . . . . . . . . . 18
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
14.1. Normative References . . . . . . . . . . . . . . . . . . 20
14.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Geometry Examples . . . . . . . . . . . . . . . . . 21
A.1. Points . . . . . . . . . . . . . . . . . . . . . . . . . 21
A.2. LineStrings . . . . . . . . . . . . . . . . . . . . . . . 21
A.3. Polygons . . . . . . . . . . . . . . . . . . . . . . . . 22
A.4. MultiPoints . . . . . . . . . . . . . . . . . . . . . . . 23
A.5. MultiLineStrings . . . . . . . . . . . . . . . . . . . . 23
A.6. MultiPolygons . . . . . . . . . . . . . . . . . . . . . . 24
A.7. GeometryCollections . . . . . . . . . . . . . . . . . . . 25
Appendix B. Changes from pre-IETF Specification . . . . . . . . 26
B.1. Normative Changes . . . . . . . . . . . . . . . . . . . . 26
B.2. Informative Changes . . . . . . . . . . . . . . . . . . . 27
Appendix C. GeoJSON Text Sequences . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
GeoJSON is a format for encoding a variety of geographic data
structures using JavaScript Object Notation (JSON) [RFC7159]. A
GeoJSON object may represent a region of space (a Geometry), a
spatially-bounded entity (a Feature), or a list of features (a
Feature Collection). GeoJSON supports the following geometry types:
Point, LineString, Polygon, MultiPoint, MultiLineString,
MultiPolygon, and GeometryCollection. Features in GeoJSON contain a
geometry object and additional properties, and a Feature Collection
contains a list of features.
The format is concerned with geographic data in the broadest sense;
any thing with qualities that are bounded in geographical space might
be a feature whether it is a physical structure or not. The concepts
in GeoJSON are not new; they are derived from pre-existing open
geographic information system standards and have been streamlined to
better suit web application development using JSON.
GeoJSON comprises the seven concrete geometry types defined in the
OpenGIS Simple Features Implementation Specification for SQL [SFSQL]:
0-dimensional Point and MultiPoint; 1-dimensional curve LineString
and MultiLineString; 2-dimensional surface Polygon and MultiPolygon;
and the heterogeneous GeometryCollection. GeoJSON representations of
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instances of these geometry types are analogous to the well-known
binary (WKB) and text (WKT) representations described in that same
specification.
GeoJSON also comprises the types Feature and FeatureCollection.
Feature objects in GeoJSON contain a geometry object with one of the
above geometry types and additional members. A FeatureCollection
object contains an array of feature objects. This structure is
analogous to that of the Web Feature Service (WFS) response to
GetFeatures requests specified in [WFSv1] or to a Keyhole Markup
Language (KML) Folder of Placemarks [KMLv2.2]. Some implementations
of the WFS specification also provide GeoJSON formatted responses to
GetFeature requests, but there is no particular service model or
feature type ontology implied in the GeoJSON format specification.
Since its initial publication in 2008 [GJ2008], the GeoJSON format
specification has steadily grown in popularity. It is widely used in
JavaScript web mapping libraries, JSON-based document databases, and
web APIs.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
1.2. Conventions Used in This Document
The ordering of the members of any JSON object defined in this
document MUST be considered irrelevant, as specified by [RFC7159].
Some examples use the combination of a JavaScript single line comment
(//) followed by an ellipsis (...) as placeholder notation for
content deemed irrelevant by the authors. These placeholders must of
course be deleted or otherwise replaced, before attempting to
validate the corresponding JSON code example.
Whitespace is used in the examples inside this document to help
illustrate the data structures, but is not required. Unquoted
whitespace is not significant in JSON.
1.3. Specification of GeoJSON
This document supersedes the original GeoJSON format specification
[GJ2008].
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1.4. Definitions
o JavaScript Object Notation (JSON), and the terms object, member,
name, value, array, number, true, false, and null are to be
interpreted as defined in [RFC7159].
o Inside this document the term "geometry type" refers to the seven
case-sensitive strings: "Point", "MultiPoint", "LineString",
"MultiLineString", "Polygon", "MultiPolygon", and
"GeometryCollection".
o As another shorthand notation, the term "GeoJSON types" refers to
the nine case-sensitive strings "Feature", "FeatureCollection" and
the geometry types listed above.
o The word "Collection" in "FeatureCollection" and
"GeometryCollection" does not have any significance for the
semantics of array members. The "features" and "geometries"
members, respectively, of these objects are standard ordered JSON
arrays, not unordered sets.
1.5. Example
A GeoJSON feature collection:
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{
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [102.0, 0.5]
},
"properties": {
"prop0": "value0"
}
}, {
"type": "Feature",
"geometry": {
"type": "LineString",
"coordinates": [
[102.0, 0.0],
[103.0, 1.0],
[104.0, 0.0],
[105.0, 1.0]
]
},
"properties": {
"prop0": "value0",
"prop1": 0.0
}
}, {
"type": "Feature",
"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": {
"this": "that"
}
}
}]
}
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2. GeoJSON Text
A GeoJSON text is a JSON text and consists of a single GeoJSON
object.
3. GeoJSON Object
A GeoJSON object represents a geometry, feature, or collection of
features.
o A GeoJSON object is a JSON object.
o A GeoJSON object has a member with the name "type". The value of
the member MUST be one of the GeoJSON types.
o A GeoJSON object MAY have a "bbox" member, the value of which MUST
be a bounding box array (see Section 5).
o A GeoJSON object MAY have other members (see Section 6).
3.1. Geometry Object
A Geometry object represents points, curves, and surfaces in
coordinate space. Every geometry object is a GeoJSON object no
matter where it occurs in a GeoJSON text.
o The value of a geometry object's "type" member MUST be one of the
seven geometry types (see Section 1.4).
o A GeoJSON geometry object of any type other than
"GeometryCollection" has a member with the name "coordinates".
The value of the coordinates member is an array. The structure of
the elements in this array is determined by the type of geometry.
GeoJSON processors MAY interpret geometry objects with empty
coordinates arrays as null objects.
3.1.1. Position
A position is the fundamental geometry construct. The "coordinates"
member of a geometry object is composed of either:
o one position in the case of a Point geometry,
o an array of positions in the case of a LineString or MultiPoint
geometry,
o an array of LineString or linear ring (see Section 3.1.6)
coordinates in the case of a Polygon or MultiLineString geometry,
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o or an array of Polygon coordinates in the case of a MultiPolygon
geometry.
A position is an array of numbers. There MUST be two or more
elements. The first two elements are longitude and latitude, or
easting and northing, precisely in that order and using decimal
numbers. Altitude or elevation MAY be included as an optional third
element.
Implementations SHOULD NOT extend positions beyond 3 elements because
the semantics of extra elements are unspecified and ambiguous.
Historically, some implementations have used a 4th element to carry a
linear referencing measure (sometimes denoted as "M") or a numerical
timestamp, but in most situations a parser will not be able to
properly interpret these values. The interpretation and meaning of
additional elements is beyond the scope of this specification and
additional elements MAY be ignored by parsers.
A line between two positions is a straight Cartesian line, the
shortest line between those two points in the Coordinate Reference
System (see Section 4).
In other words, every point on a line that does not cross the
antimeridian between a point (lon0, lat0) and (lon1, lat1) can be
calculated as
F(lon, lat) = (lon0 + (lon1 - lon0) * t, lat0 + (lat1 - lat0) * t)
with t a real number greater or equal to 0 and smaller or equal to 1.
Note that this line may markedly differ from the geodesic path along
the curved surface of the reference ellipsoid.
The same applies to the optional height element with the proviso that
the direction of the height is as specified in the Coordinate
Reference System.
Note that, again, this does not mean that a surface with equal height
follows, for example, the curvature of a body of water. Nor is a
surface of equal height perpendicular to a plumb line.
Examples of positions and geometries are provided in "Appendix A.
Geometry Examples".
3.1.2. Point
For type "Point", the "coordinates" member is a single position.
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3.1.3. MultiPoint
For type "MultiPoint", the "coordinates" member is an array of
positions.
3.1.4. LineString
For type "LineString", the "coordinates" member is an array of two or
more positions.
3.1.5. MultiLineString
For type "MultiLineString", the "coordinates" member is an array of
LineString coordinate arrays.
3.1.6. Polygon
To specify a constraint specific to polygons, it is useful to
introduce the concept of a linear ring:
o A linear ring is a closed LineString with 4 or more positions.
o The first and last positions are equivalent, they MUST contain
identical values; their representation SHOULD also be identical.
o A linear ring is the boundary of a surface or the boundary of a
hole in a surface.
o A linear ring MUST follow the right-hand rule with respect to the
area it bounds (i.e., exterior rings are counter-clockwise, holes
are clockwise).
Note: the [GJ2008] specification did not discuss linear ring winding
order. For backwards compatibility, parsers SHOULD NOT reject
polygons that do not follow the right-hand rule.
Though a linear ring is not explicitly represented as a GeoJSON
geometry type, it leads to a canonical formulation of the Polygon
geometry type definition as follows:
o For type "Polygon", the "coordinates" member MUST be an array of
linear ring coordinate arrays.
o For Polygons with more than one of these rings, the first MUST be
the exterior ring and any others MUST be interior rings. The
exterior ring bounds the surface, and the interior rings (if
present) bound holes within the surface.
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3.1.7. MultiPolygon
For type "MultiPolygon", the "coordinates" member is an array of
Polygon coordinate arrays.
3.1.8. Geometry Collection
A GeoJSON object with type "GeometryCollection" is a geometry object.
A geometry collection has a member with the name "geometries". The
value of "geometries" is an array. Each element of this array is a
GeoJSON geometry object. It is possible for this array to be empty.
Unlike the other geometry types described above, a geometry
collection can be a heterogeneous composition of smaller geometry
objects. For example, a geometry object in the shape of a lowercase
roman "i" can be composed of one point and one line string.
Geometry collections have a different syntax from single type
geometry objects (Point, LineString, and Polygon) and homogeneously
typed multipart geometry objects (MultiPoint, MultiLineString, and
MultiPolygon) but have no different semantics. Although a geometry
collection object has no "coordinates" member, it does have
coordinates: the coordinates of all its parts belong to the
collection. The "geometries" member of a geometry collection
describes the parts of this composition. Implementations SHOULD NOT
apply any additional semantics to the "geometries" array.
To maximize interoperability implementations SHOULD avoid nested
geometry collections. Furthermore, geometry collections composed of
a single part or a number of parts of a single type SHOULD be avoided
when that single part or a single object of multi-part type
(MultiPoint, MultiLineString, or MultiPolygon) could be used instead.
3.1.9. Antimeridian Cutting
In representing features that cross the antimeridian,
interoperability is improved by modifying their geometry. Any
geometry that crosses the antimeridian SHOULD be represented by
cutting it in two such that neither part's representation crosses the
antimeridian.
For example, a line extending from 45 degrees N, 170 degrees E across
the antimeridian to 45 degrees N, 170 degrees W should be cut in two
and represented as a MultiLineString.
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{
"type": "MultiLineString",
"coordinates": [
[
[170.0, 45.0], [180.0, 45.0]
], [
[-180.0, 45.0], [-170.0, 45.0]
]
]
}
A rectangle extending from 40 degrees N, 170 degrees E across the
antimeridian to 50 degrees N, 170 degrees W should be cut in two and
represented as a MultiPolygon.
{
"type": "MultiPolygon",
"coordinates": [
[
[
[180.0, 40.0], [180.0, 50.0], [170.0, 50.0],
[170.0, 40.0], [180.0, 40.0]
]
],
[
[
[-170.0, 40.0], [-170.0, 50.0], [-180.0, 50.0],
[-180.0, 40.0], [-170.0, 40.0]
]
]
]
}
3.1.10. Uncertainty and Precision
As in [RFC5870] the number of digits of the values in coordinate
positions MUST NOT be interpreted as an indication to the level of
uncertainty.
3.2. Feature Object
A Feature object represents a spatially-bounded thing. Every feature
object is a GeoJSON object no matter where it occurs in a GeoJSON
text.
o A feature object has a "type" member with the value "Feature".
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o A feature object has a member with the name "geometry". The value
of the geometry member SHALL be either a geometry object as
defined above or, in the case that the feature is unlocated, a
JSON null value.
o A feature object has a member with the name "properties". The
value of the properties member is an object (any JSON object or a
JSON null value).
o If a feature has a commonly used identifier, that identifier
SHOULD be included as a member of the feature object with the name
"id", and the value of this member is either a JSON string or
number.
3.3. Feature Collection Object
A GeoJSON object with the type "FeatureCollection" is a feature
collection object. A feature collection object has a member with the
name "features". The value of "features" is a JSON array. Each
element of the array is a feature object as defined above. It is
possible for this array to be empty.
4. Coordinate Reference System
The coordinate reference system for all GeoJSON coordinates is a
geographic coordinate reference system, using the WGS 84 [WGS84]
datum, and with longitude and latitude units of decimal degrees.
This is equivalent to the coordinate reference system identified by
the OGC URN urn:ogc:def:crs:OGC::CRS84. An OPTIONAL third position
element SHALL be the height in meters above or below the WGS 84
reference ellipsoid. In the absence of elevation values,
applications sensitive to height or depth SHOULD interpret positions
as being at local ground or sea level.
Note: the use of alternative coordinate reference systems was
specified in [GJ2008], but has been removed from this version of the
specification because the use of different coordinate reference
systems -- especially in the manner specified in [GJ2008] -- has
proven to have interoperability issues. In general, GeoJSON
processing software is not expected to have access to coordinate
reference systems databases or to have network access to coordinate
reference system transformation parameters. However, where all
involved parties have a prior arrangement, alternative coordinate
reference systems can be used without risk of data being
misinterpreted.
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5. Bounding Box
A GeoJSON object MAY have a member named "bbox" to include
information on the coordinate range for its geometries, features, or
feature collections. The value of the bbox member MUST be an array
of length 2*n where n is the number of dimensions represented in the
contained geometries, with all axes of the most south-westerly point
followed by all axes of the more north-easterly point. The axes
order of a bbox follows the axes order of geometries.
The "bbox" values define shapes with edges that follow lines of
constant longitude, latitude, and elevation.
Example of a 2D bbox member on a feature:
{
"type": "Feature",
"bbox": [-10.0, -10.0, 10.0, 10.0],
"geometry": {
"type": "Polygon",
"coordinates": [
[
[-10.0, -10.0],
[10.0, -10.0],
[10.0, 10.0],
[-10.0, -10.0]
]
]
}
//...
}
Example of a 2D bbox member on a feature collection:
{
"type": "FeatureCollection",
"bbox": [100.0, 0.0, 105.0, 1.0],
"features": [
//...
]
}
Example of a 3D bbox member with a depth of 100 meters:
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{
"type": "FeatureCollection",
"bbox": [100.0, 0.0, -100.0, 105.0, 1.0, 0.0],
"features": [
//...
]
}
5.1. The Connecting Lines
The 4 lines of the bounding box are defined fully within the
coordinate reference system; i.e. for a box bounded by the values
"west", "south", "east", and "north" every point on the northernmost
line can be expressed as
(lon, lat) = (west + (east - west) * t, north)
with 0 <= t <= 1.
5.2. The Antimeridian
Consider a set of point features within the Fiji archipelago,
straddling the antimeridian between 16 degrees S and 20 degrees S.
The southwest corner of the box containing these features is at 20
degrees S and 177 degrees E, the northwest corner is at 16 degrees S
and 178 degrees W. The antimeridian-spanning GeoJSON bounding box
for this feature collection is
"bbox": [177.0, -20.0, -178.0, -16.0]
and covers 5 degrees of longitude.
The complementary bounding box for the same latitude band, not
crossing the antimeridian, is
"bbox": [-178.0, -20.0, 177.0, -16.0]
and covers 355 degrees of longitude.
The latitude of the northeast corner is always greater than the
latitude of the southwest corner, but bounding boxes that cross the
antimeridian have a northeast corner longitude that is less than the
longitude of the southwest corner.
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5.3. The Poles
A bounding box that contains the North Pole extends from a southwest
corner of "minlat" degrees N, 180 degrees W to a northeast corner of
90 degrees N, 180 degrees E. Viewed on a globe, this bounding box
approximates a spherical cap bounded by the "minlat" circle of
latitude.
"bbox": [-180.0, minlat, 180.0, 90.0]
A bounding box that contains the South Pole extends from a southwest
corner of 90 degrees S, 180 degrees W to a northeast corner of
"maxlat" degrees S, 180 degrees E.
"bbox": [-180.0, -90.0, 180.0, maxlat]
A bounding box that just touches the North Pole and forms a slice of
an approximate spherical cap when viewed on a globe extends from a
southwest corner of "minlat" degrees N and "westlon" degrees E to a
northeast corner of 90 degrees N and "eastlon" degrees E.
"bbox": [westlon, minlat, eastlon, 90.0]
Similarly, a bounding box that just touches the South Pole and forms
a slice of an approximate spherical cap when viewed on a globe has
the following representation in GeoJSON.
"bbox": [westlon, -90.0, eastlon, maxlat]
Implementers MUST NOT use latitude values greater than 90 or less
than -90 to imply an extent that is not a spherical cap.
6. Extending GeoJSON
6.1. Foreign Members
Members not described in this specification ("foreign members") MAY
be used in a GeoJSON document. Note that support for foreign members
can vary across implementations and no normative processing model for
foreign members is defined. Accordingly, implementations that rely
too heavily on the use of foreign members might experience reduced
interoperability with other implementations.
For example, in the (abridged) feature object shown below
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{
"type": "Feature",
"id": "f1",
"geometry": {...},
"properties": {...},
"title": "Example Feature"
}
the name/value pair of "title": "Example Feature" is a foreign
member. When the value of a foreign member is an object, all the
descendant members of that object are themselves foreign members.
GeoJSON semantics do not apply to foreign members and their
descendants, regardless of their names and values. For example, in
the (abridged) feature object below
{
"type": "Feature",
"id": "f2",
"geometry": {...},
"properties": {...},
"centerline": {
"type": "LineString",
"coordinates": [
[-170, 10],
[170, 11]
]
}
}
the "centerline" member is not a GeoJSON geometry object.
7. GeoJSON Types are not Extensible
Implementations MUST NOT extend the fixed set of GeoJSON types:
FeatureCollection, Feature, Point, LineString, MultiPoint, Polygon,
MultiLineString, MultiPolygon, and GeometryCollection.
7.1. Semantics of GeoJSON Members and Types are not Changeable
Implementations MUST NOT change the semantics of GeoJSON members and
types.
The GeoJSON "coordinates" and "geometries" members define Geometry
objects. FeatureCollection and Feature objects, respectively, MUST
NOT contain a "coordinates" or "geometries" member.
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The GeoJSON "geometry" and "properties" members define a Feature
object. FeatureCollection and Geometry objects, respectively, MUST
NOT contain a "geometry" or "properties" member.
The GeoJSON "features" member defines a FeatureCollection object.
Feature and Geometry objects, respectively, MUST NOT contain a
"features" member.
8. Versioning
The GeoJSON format can be extended as defined here, but no explicit
versioning scheme is defined. A specification that alters the
semantics of GeoJSON members or otherwise modifies the format does
not create a new version of this format; instead, it defines an
entirely new format that MUST NOT be identified as GeoJSON.
9. Mapping 'geo' URIs
'geo' URIs [RFC5870] identify geographic locations and precise (not
uncertain) locations can be mapped to GeoJSON geometry objects.
For this section, as in [RFC5870], "lat", "lon", "alt", and "unc" are
placeholders for 'geo' URI latitude, longitude, altitude, and
uncertainty values, respectively.
A 'geo' URI with two coordinates and an uncertainty ('u') parameter
that is absent or zero, and a GeoJSON Point geometry may be mapped to
each other. A GeoJSON point is always converted to a 'geo' URI that
has no uncertainty parameter.
'geo' URI:
geo:lat,lon
GeoJSON:
{"type": "Point", "coordinates": [lon, lat]}
The mapping between 'geo' URIs and GeoJSON points that specify
elevation is shown below.
'geo' URI:
geo:lat,lon,alt
GeoJSON:
{"type": "Point", "coordinates": [lon, lat, alt]}
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GeoJSON has no concept of uncertainty; imprecise or uncertain 'geo'
URIs thus cannot be mapped to GeoJSON geometries.
10. Security Considerations
GeoJSON shares security issues common to all JSON content types. See
[RFC7159] Section 12 for additional information. GeoJSON does not
provide executable content.
GeoJSON does not provide privacy or integrity services. If sensitive
data requires privacy or integrity protection, those must be provided
by the transport -- for example TLS or HTTPS. There will be cases in
which stored data need protection, which is out of scope for this
document.
As with other geographic data formats, e.g., [KMLv2.2], providing
details about the locations of sensitive persons, animals, habitats,
and facilities can expose them to unauthorized tracking or injury.
Data providers should recognize the risk of inadvertantly identifying
individuals if locations in anonymized datasets are not adequately
skewed or not sufficiently fuzzed [Sweeney] and recognize that the
effectiveness of location obscuration is limited by a number of
factors and is unlikely to be an effective defense against a
determined attack [RFC6772].
11. Interoperability Considerations
11.1. I-JSON
GeoJSON texts should follow the constraints of I-JSON [RFC7493] for
maximum interoperability.
11.2. Coordinate Precision
The size of a GeoJSON text in bytes is a major interoperability
consideration and precision of coordinate values has a large impact
on the size of texts. A GeoJSON text containing many detailed
polygons can be inflated almost by a factor of two by increasing
coordinate precision from 6 to 15 decimal places. For geographic
coordinates with units of degrees, 6 decimal places (a default common
in, e.g., sprintf) amounts to about 10 centimeters, a precision well
within that of current GPS systems. Implementations should consider
the cost of using a greater precision than necessary.
Furthermore the WGS 84 [WGS84] datum is a relatively coarse
approximation of the geoid; with the height varying by up to 5m (but
generally between 2 and 3 meters) higher or lower relative to a
surface parallel to Earth's mean sea level.
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12. IANA Considerations
The media type for GeoJSON text is "application/geo+json" and is
registered in the "Media Types" registry described in [RFC6838]. The
entry for "application/vnd.geo+json" in the same registry should have
its status changed to be Obsolete with a pointer to the media type
"application/geo+json" and a reference added to this RFC.
Type name: application
Subtype name: geo+json
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: binary
Security considerations: See Section 10 above
Interoperability considerations: See Section 11 above
Published specification: [[This document]]
Applications that use this media type: No known applications
currently use this media type. This media type is intended for
GeoJSON applications currently using the "application/
vnd.geo+json" or "application/json" media types, of which there
are several categories: web mapping, geospatial databases,
geographic data processing APIs, data analysis and storage
services, and data dissemination.
Additional information:
Magic number(s): n/a
File extension(s): .json, .geojson
Macintosh file type code: n/a
Object Identifiers: n/a
Windows clipboard name: GeoJSON
Macintosh uniform type identifier: public.geojson conforms to
public.json
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Person to contact for further information: Sean Gillies
(sean.gillies@gmail.com)
Intended usage: COMMON
Restrictions on usage: none
Restrictions on usage: none
Author: see "Authors' Addresses" section of [[This document]].
Change controller: Internet Engineering Task Force
13. Acknowledgements
The GeoJSON format is the product of discussion on the GeoJSON
mailing list, http://lists.geojson.org/listinfo.cgi/geojson-
geojson.org, before October 2015 and the IETF's GeoJSON WG after
October 2015.
Material in this document was adapted with changes from
http://geojson.org/geojson-spec.html [GJ2008] which is licensed under
http://creativecommons.org/licenses/by/3.0/us/.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<http://www.rfc-editor.org/info/rfc7493>.
[WGS84] National Imagery and Mapping Agency, "Department of
Defense World Geodetic System 1984, Third Edition", 1984.
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14.2. Informative References
[GJ2008] Butler, H., Daly, M., Doyle, A., Gillies, S., Schaub, T.,
and C. Schmidt, "The GeoJSON Format Specification", June
2008.
[KMLv2.2] Wilson, T., "OGC KML", OGC 07-147r2, April 2008.
[RFC6772] Schulzrinne, H., Ed., Tschofenig, H., Ed., Cuellar, J.,
Polk, J., Morris, J., and M. Thomson, "Geolocation Policy:
A Document Format for Expressing Privacy Preferences for
Location Information", RFC 6772, DOI 10.17487/RFC6772,
January 2013, <http://www.rfc-editor.org/info/rfc6772>.
[RFC7464] Williams, N., "JavaScript Object Notation (JSON) Text
Sequences", RFC 7464, DOI 10.17487/RFC7464, February 2015,
<http://www.rfc-editor.org/info/rfc7464>.
[SFSQL] OpenGIS Consortium, Inc., "OpenGIS Simple Features
Specification For SQL Revision 1.1", OGC 99-049, May 1999.
[Sweeney] Sweeney, L., "k-anonymity: a model for protecting
privacy", International Journal on Uncertainty, Fuzziness
and Knowledge-based Systems 10 (5), 2002; 557-570, 2002.
[WFSv1] Vretanos, P., "Web Feature Service Implementation
Specification", OGC 02-058, May 2002.
Appendix A. Geometry Examples
Each of the examples below represents a valid and complete GeoJSON
object.
A.1. Points
Point coordinates are in x, y order (easting, northing for projected
coordinates, longitude, latitude for geographic coordinates):
{
"type": "Point",
"coordinates": [100.0, 0.0]
}
A.2. LineStrings
Coordinates of LineString are an array of positions (see
Section 3.1.1):
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{
"type": "LineString",
"coordinates": [
[100.0, 0.0],
[101.0, 1.0]
]
}
A.3. Polygons
Coordinates of a Polygon are an array of LinearRing (see
Section 3.1.6) coordinate arrays. The first element in the array
represents the exterior ring. Any subsequent elements represent
interior rings (or holes).
No holes:
{
"type": "Polygon",
"coordinates": [
[
[100.0, 0.0],
[100.0, 1.0],
[101.0, 1.0],
[101.0, 0.0],
[100.0, 0.0]
]
]
}
With holes:
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{
"type": "Polygon",
"coordinates": [
[
[100.0, 0.0],
[100.0, 1.0],
[101.0, 1.0],
[101.0, 0.0],
[100.0, 0.0]
],
[
[100.8, 0.8],
[100.2, 0.8],
[100.2, 0.2],
[100.8, 0.2],
[100.8, 0.8]
]
]
}
A.4. MultiPoints
Coordinates of a MultiPoint are an array of positions::
{
"type": "MultiPoint",
"coordinates": [
[100.0, 0.0],
[101.0, 1.0]
]
}
A.5. MultiLineStrings
Coordinates of a MultiLineString are an array of LineString
coordinate arrays:
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{
"type": "MultiLineString",
"coordinates": [
[
[100.0, 0.0],
[101.0, 1.0]
],
[
[102.0, 2.0],
[103.0, 3.0]
]
]
}
A.6. MultiPolygons
Coordinates of a MultiPolygon are an array of Polygon coordinate
arrays:
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{
"type": "MultiPolygon",
"coordinates": [
[
[
[102.0, 2.0],
[102.0, 3.0],
[103.0, 3.0],
[103.0, 2.0],
[102.0, 2.0]
]
],
[
[
[100.0, 0.0],
[100.0, 1.0],
[101.0, 1.0],
[101.0, 0.0],
[100.0, 0.0]
],
[
[100.2, 0.2],
[100.8, 0.2],
[100.8, 0.8],
[100.2, 0.8],
[100.2, 0.2]
]
]
]
}
A.7. GeometryCollections
Each element in the geometries array of a GeometryCollection is one
of the geometry objects described above:
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{
"type": "GeometryCollection",
"geometries": [{
"type": "Point",
"coordinates": [100.0, 0.0]
}, {
"type": "LineString",
"coordinates": [
[101.0, 0.0],
[102.0, 1.0]
]
}]
}
Appendix B. Changes from pre-IETF Specification
This appendix briefly summarizes non-editorial changes from the 2008
specification [GJ2008].
B.1. Normative Changes
o Specification of coordinate reference systems has been removed,
i.e., the "crs" member of [GJ2008] is no longer used.
o In the absence of elevation values, applications sensitive to
height or depth SHOULD interpret positions as being at local
ground or sea level (see Section 4).
o Implementations SHOULD NOT extend position arrays beyond 3
elements (see Section 3.1.1).
o A line between two positions is a straight Cartesian line (see
Section 3.1.1).
o Polygon rings MUST follow the right-hand rule for orientation
(counter-clockwise external rings, clockwise internal rings).
o The values of a "bbox" array are "[west, south, east, north]", not
"[minx, miny, maxx, maxy]" (see Section 5).
o A Feature object's "id" member is a string or number (see
Section 3.2).
o Extensions MAY be used, but MUST NOT change the semantics of
GeoJSON members and types (see Section 6).
o GeoJSON objects MUST NOT contain the defining members of other
types (see Section 7.1).
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o The media type for GeoJSON is application/geo+json.
B.2. Informative Changes
o The definition of a GeoJSON text has been added.
o Rules for mapping 'geo' URIs have been added.
o A recommendation of the I-JSON [RFC7493] constraints has been
added.
o Implementers are cautioned about the effect of excessive
coordinate precision on interoperability.
o Interoperability concerns of geometry collections are noted.
These objects should be used sparingly (see Section 3.1.8).
Appendix C. GeoJSON Text Sequences
All GeoJSON objects defined in this specification -
FeatureCollection, Feature, and Geometry - consist of exactly one
JSON object. However, there may be circumstances in which
applications need to represent sets or sequences of these objects
(over and above the grouping of Feature objects in a
FeatureCollection), e.g. in order to efficiently "stream" large
numbers of Feature objects. The definition of such sets or sequences
is outside the scope of this specification.
If such a representation is needed, a new media type is required that
has the ability to represent these sets or sequences. When defining
such a media type, it may be useful to base it on "JSON Text
Sequences" [RFC7464], leaving the foundations of how to represent
multiple JSON objects to that specification, and only defining how it
applies to GeoJSON objects.
Authors' Addresses
H. Butler
Hobu Inc.
Email: howard@hobu.co
M. Daly
Cadcorp
Email: martin.daly@cadcorp.com
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A. Doyle
Email: adoyle@intl-interfaces.com
S. Gillies
Mapbox
Email: sean.gillies@gmail.com
URI: http://sgillies.net
S. Hagen
Rheinaustr. 62
Bonn 53225
DE
Email: stefan@hagen.link
URI: http://stefan-hagen.website/
T. Schaub
Planet Labs
Email: tim.schaub@gmail.com
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