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Versions: (draft-butler-geojson) 00 01 02 03 04 RFC 7946

GeoJSON                                                        H. Butler
Internet-Draft                                                 Hobu Inc.
Intended status: Standards Track                                 M. Daly
Expires: November 14, 2016                                       Cadcorp
                                                                A. Doyle

                                                              S. Gillies
                                                                  Mapbox
                                                                S. Hagen

                                                               T. Schaub
                                                             Planet Labs
                                                            May 13, 2016


                           The GeoJSON Format
                         draft-ietf-geojson-03

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.
   This document recommends a single coordinate reference system based
   on WGS 84.  Other coordinate reference systems are not recommended.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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 November 14, 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 Confidence  . . . . . . . . . . . . .  11
     3.2.  Feature Object  . . . . . . . . . . . . . . . . . . . . .  12
     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 . . . . . . . . . . . . . . . . . . . . .  18
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     14.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Appendix A.  Geometry Examples  . . . . . . . . . . . . . . . . .  21
     A.1.  Points  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     A.2.  LineStrings . . . . . . . . . . . . . . . . . . . . . . .  21
     A.3.  Polygons  . . . . . . . . . . . . . . . . . . . . . . . .  21
     A.4.  MultiPoints . . . . . . . . . . . . . . . . . . . . . . .  22
     A.5.  MultiLineStrings  . . . . . . . . . . . . . . . . . . . .  23
     A.6.  MultiPolygons . . . . . . . . . . . . . . . . . . . . . .  23
     A.7.  GeometryCollections . . . . . . . . . . . . . . . . . . .  24
   Appendix B.  Changes from pre-IETF Specification  . . . . . . . .  25
     B.1.  Normative Changes . . . . . . . . . . . . . . . . . . . .  25
     B.2.  Informative Changes . . . . . . . . . . . . . . . . . . .  26
   Appendix C.  GeoJSON Text Sequences . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

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 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 updates 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 MUST have 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 any number of other members (see
      Section 6).

3.1.  Geometry Object

   A Geometry object represents points, curves, and surfaces in
   coordinate space.

   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" MUST have a member with the name
      "coordinates".  The value of the coordinates member is always 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 MUST be a single position.





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3.1.3.  MultiPoint

   For type "MultiPoint", the "coordinates" member MUST be an array of
   positions.

3.1.4.  LineString

   For type "LineString", the "coordinates" member MUST be an array of
   two or more positions.

3.1.5.  MultiLineString

   For type "MultiLineString", the "coordinates" member MUST be 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 SHOULD follow the right-hand rule with respect to
      the area it bounds (i.e., exterior rings are counter-clockwise,
      holes are clockwise)

   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 MUST be an array of
   Polygon coordinate arrays.

3.1.8.  Geometry Collection

   A GeoJSON object with type "GeometryCollection" is a geometry object.
   A geometry collection MUST have 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 Confidence

   As per [RFC7459] no measure of location uncertainty or confidence can
   be known for "Point", "MultiPoint", "LineString", or
   "MultiLineString" geometry types.

   Applications such as PIDF-LO that are sensitive to location
   uncertainty and confidence might treat a geometry object of type
   "Polygon", "MultiPolygon", and "GeometryCollection" as a
   representation of a 95% confidence surface.  In probabilistic terms:
   95 percent of the location's point set is contained within the
   GeoJSON geometry.






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   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.

   o  A feature object MUST have a "type" member with the value
      "Feature".

   o  A feature object MUST have a member with the name "geometry".  The
      value of the geometry member SHALL be either a geometry object as
      defined above or, in the the case that the feature is unlocated, a
      JSON null value.

   o  A feature object MUST have 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 MUST have 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 coordinate reference system is equivalent to the OGC's "http://
   www.opengis.net/def/crs/OGC/1.3/CRS84" [OGCURL].  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



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   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 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.

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:









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   {
       "type": "FeatureCollection",
       "bbox": [100.0, 0.0, 105.0, 1.0],
       "features": [
       //...
       ]
   }

   Example of a 3D bbox member with a depth of 100 meters:

   {
       "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. every point on the northernmost
   line can be expressed as

   (lon, lat) = (%minlon% + (%maxlon% - %minlon%) * t, %maxlat%)

   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.




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   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.

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.

   "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 has as its
   northeast corner coordinates the easternmost longitude value and 90
   degrees N.

   "bbox": [%westlon%, %minlat%, %eastlon%, 90.0]

   A bounding box that just touches the South Pole and forms a slice of
   an approximate spherical cap when viewed on a globe has as its
   southwest corner coordinates the westernmost longitude value and 90
   degrees S.

   "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.




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   For example, in the (abridged) feature object shown below

   {
       "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 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 can not 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.

   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.
   GeoJSON does not provide privacy or integrity services; if sensitive
   data requires privacy or integrity protection the service must be
   provided externally.

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.

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.




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   Type name:  application

   Subtype name:  geo+json

   Required parameters:  n/a

   Optional parameters:  n/a

   Encoding considerations:  binary

   Security considerations:  See section 9 above

   Interoperability considerations:  See section 10 above

   Published specification:  [[This document]]

   Applications that use this media type:  various

   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

   Person to contact for further information:  Sean Gillies
      (sean.gillies@gmail.com)

   Intended usage:  COMMON

   Restrictions on usage:  none

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.





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   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.

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.

   [OGCURL]   Cox, S., "OGC-NA Name type specification - definitions:
              Part 1 - basic name", OGC 09-048r3, March 2010.

   [RFC7459]  Thomson, M. and J. Winterbottom, "Representation of
              Uncertainty and Confidence in the Presence Information
              Data Format Location Object (PIDF-LO)", RFC 7459, DOI
              10.17487/RFC7459, February 2015,
              <http://www.rfc-editor.org/info/rfc7459>.

   [RFC7464]  Williams, N., "JavaScript Object Notation (JSON) Text
              Sequences", RFC 7464, DOI 10.17487/RFC7464, February 2015,
              <http://www.rfc-editor.org/info/rfc7464>.




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   [SFSQL]    OpenGIS Consortium, Inc., "OpenGIS Simple Features
              Specification For SQL Revision 1.1", OGC 99-049, May 1999.

   [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):

     {
         "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:









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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]
             ]
         ]
     }

   With holes:

     {
         "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]
         ]
     }





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A.5.  MultiLineStrings

   Coordinates of a MultiLineString are an array of LineString
   coordinate arrays:

     {
         "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  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 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).

   o  The media type for GeoJSON is application/geo+json.




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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  Right-hand rule orientation of polygon rings (counter-clockwise
      external rings, clockwise internal rings) is recommended to
      improve 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








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   M. Daly
   Cadcorp

   Email: martin.daly@cadcorp.com


   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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