The GeoJSON Format
draft-butler-geojson-05
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | H. Butler , M. Daly , A. Doyle , Sean Gillies , Stefan Hagen | ||
| Last updated | 2015-01-28 | ||
| Replaced by | draft-ietf-geojson, RFC 7946 | ||
| RFC stream | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-butler-geojson-05
Independent H. Butler
Internet-Draft Hobu Inc.
Intended status: Informational M. Daly
Expires: August 1, 2015 Cadcorp
A. Doyle
MIT
S. Gillies
Mapbox Inc.
T. Schaub
OpenGeo
S. Drees
January 28, 2015
The GeoJSON Format
draft-butler-geojson-05
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 August 1, 2015.
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Copyright Notice
Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . 3
1.2. Conventions Used in This Document . . . . . . . . . . . . 4
1.3. Specification of GeoJSON . . . . . . . . . . . . . . . . 4
1.4. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
1.5. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. GeoJSON Object . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Geometry Object . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Position . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2. Point . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.3. MultiPoint . . . . . . . . . . . . . . . . . . . . . 7
2.1.4. LineString . . . . . . . . . . . . . . . . . . . . . 7
2.1.5. MultiLineString . . . . . . . . . . . . . . . . . . . 7
2.1.6. Polygon . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.7. MultiPolygon . . . . . . . . . . . . . . . . . . . . 8
2.1.8. Geometry Collection . . . . . . . . . . . . . . . . . 8
2.2. Feature Object . . . . . . . . . . . . . . . . . . . . . 8
2.3. Feature Collection Object . . . . . . . . . . . . . . . . 8
3. Coordinate Reference System . . . . . . . . . . . . . . . . . 8
4. Bounding Box . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Interoperability Considerations . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Geometry Examples . . . . . . . . . . . . . . . . . 13
A.1. Points . . . . . . . . . . . . . . . . . . . . . . . . . 13
A.2. LineStrings . . . . . . . . . . . . . . . . . . . . . . . 13
A.3. Polygons . . . . . . . . . . . . . . . . . . . . . . . . 13
A.4. MultiPoints . . . . . . . . . . . . . . . . . . . . . . . 15
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A.5. MultiLineStrings . . . . . . . . . . . . . . . . . . . . 15
A.6. MultiPolygons . . . . . . . . . . . . . . . . . . . . . . 16
A.7. GeometryCollections . . . . . . . . . . . . . . . . . . . 17
Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
GeoJSON is a format for encoding data about geographic features using
JavaScript Object Notation (JSON) [RFC7159]. The format is concerned
with features in the broadest sense; any thing with qualities that
are bounded in geographical space may 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 (for COM, SQL, and XML) 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
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 properties. 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].
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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].
1.4. Definitions
o JavaScript Object Notation (JSON), and the terms object, 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.
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 Object
GeoJSON always consists of a single object. This object (referred to
as the GeoJSON object below) represents a geometry, feature, or
collection of features.
o The GeoJSON object MUST have a member with the name "type". The
value of the member MUST be one of the GeoJSON types.
o The GeoJSON object MAY have any number of other members.
o A GeoJSON object MAY have a "bbox" member, the value of which MUST
be a bounding box array (see 4. Bounding Boxes).
2.1. Geometry Object
A geometry object is a GeoJSON object where the "type" value is one
of the geometry types. 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.
2.1.1. 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 (LineString or MultiPoint geometries),
o an array of arrays of positions (Polygons, MultiLineStrings),
o or a multidimensional array of positions (MultiPolygon).
A position is represented by an array of numbers. There MUST be two
or more elements. The first two elements will be 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.
Additional position elements MAY be included but MUST follow the
three specified above and MAY be ignored by software. Interpretation
and meaning of additional elements is beyond the scope of this
specification.
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Examples of positions and geometries are provided in "Appendix A.
Geometry Examples".
2.1.2. Point
For type "Point", the "coordinates" member MUST be a single position.
2.1.3. MultiPoint
For type "MultiPoint", the "coordinates" member MUST be an array of
positions.
2.1.4. LineString
For type "LineString", the "coordinates" member MUST be an array of
two or more positions.
2.1.5. MultiLineString
For type "MultiLineString", the "coordinates" member MUST be an array
of LineString coordinate arrays.
2.1.6. 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 represent
equivalent points).
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 right-hand rule with respect to the
area it bounds (ie. 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
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exterior ring bounds the surface and the interiors rings (if
present) bound holes within the surface.
2.1.7. MultiPolygon
For type "MultiPolygon", the "coordinates" member MUST be an array of
Polygon coordinate arrays.
2.1.8. Geometry Collection
A GeoJSON object with type "GeometryCollection" is a geometry object
which represents a collection of geometry objects. A geometry
collection MUST have a member with the name "geometries". The value
corresponding to "geometries" is an array. Each element in this
array is a GeoJSON geometry object.
2.2. Feature Object
A GeoJSON object with the type "Feature" is a feature object.
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.
2.3. Feature Collection Object
A GeoJSON object with the type "FeatureCollection" is a feature
collection object. An object of type "FeatureCollection" MUST have a
member with the name "features". The value corresponding to
"features" is an array. Each element in the array is a feature
object as defined above.
3. Coordinate Reference System
The default reference system for all GeoJSON coordinates SHALL be a
geographic coordinate reference system, using the [WGS84] datum, and
with longitude and latitude units of decimal degrees. This
coordinate reference system is equivalent to the OGC's
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"http://www.opengis.net/def/crs/OGC/1.3/CRS84" [OGCURL]. An OPTIONAL
third position element SHALL be the height in meters above the WGS 84
reference ellipsoid. For widest interoperability, GeoJSON data
SHOULD use this default coordinate reference system.
Other coordinate reference systems, including ones described by CRS
objects of the kind defined in [GJ2008] are NOT RECOMMENDED. GeoJSON
processing software SHALL NOT be expected to have access to
coordinate reference systems databases. Applications requiring CRS
other than the default MUST assume all responsibility for reference
system and coordinate accuracy. Furthermore, GeoJSON coordinates
MUST NOT under any circumstances use latitude, longitude order. See
Section 6, Interoperability Considerations, for guidance in
processing GeoJSON documents that do contain such a CRS object.
4. 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 for 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.
Example of a bbox member on a feature:
{
"type": "Feature",
"bbox": [-180.0, -90.0, 180.0, 90.0],
"geometry": {
"type": "Polygon",
"coordinates": [
[
[-180.0, 10.0],
[20.0, 90.0],
[180.0, -5.0],
[-30.0, -90.0]
]
]
}
//...
}
Example of a 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 bbox for line crossing the date-line:
{
"type": "Feature",
"bbox": [170, 10, -170, 11],
"geometry": {
"type": "LineString",
"coordinates": [
[-170, 10],
[170, 11]
]
}
//...
}
5. 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.
6. Interoperability Considerations
There is a difference of opinion among geographic data formats over
whether latitude or longitude come first in a pair of numbers.
Longitude comes first in GeoJSON coordinates as it does in [KMLv2.2].
Some commonly-used CRS definitions specify coordinate ordering that
is not longitude then latitude (for a geographic CRS) or easting then
northing (for a projected CRS). The CRS historically known as
"EPSG:4326" and more accurately named
"http://www.opengis.net/def/crs/EPSG/0/4326" is a prime example.
Using such a CRS is NOT RECOMMENDED due to the potential disruption
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of interoperability. When such a CRS is encountered in GeoJSON, the
document should be processed with caution. Heuristics may be
necessary to interpret the coordinates properly; they may not be in
the required longitude, latitude order.
Earlier versions of the GeoJSON specification recommended use of OGC
URNs such as "urn:ogc:def:crs:OGC:1.3:CRS84" to name a CRS. This
version deprecates the URNs and recommends a change to HTTP URLs
[Section 3.1]. Widely deployed systems using, e.g. the GDAL and OGR
libraries, currently write the deprecated OGC URNs into GeoJSON
documents and will do so until replaced by newer versions. GeoJSON
processors should be prepared for either form.
In representing features that cross the dateline or the poles,
following the ring-orientation best practice (counter-clockwise
external rings, clockwise internal rings) and ensuring your bounding
boxes use the south-west corner as the first coordinate will improve
interoperability. Remain aware that software that represents edges
as straight cartesian lines and software that represents edges as
great circles will have different interpretations of edges, which
vary more the longer the edges are. Try to avoid edges of more than
180 degrees in length as far as possible.
7. IANA Considerations
The MIME media type for GeoJSON text is application/vnd.geo+json.
Type name: application
Subtype name: vnd.geo+json
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: binary
Security considerations: See section 5 above
Interoperability considerations: See section 6 above
Published specification: draft-butler-geojson
Applications that use this media type: various
Additional information:
Magic number(s) : n/a
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File extension(s) : .json, .geojson
Macintosh file type code : TEXT
Object Identifiers: n/a
Person to contact for further information:
Sean Gillies
sean.gillies@gmail.com
Intended usage: COMMON
Restrictions on usage: none
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
8.2. 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.
[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.
[WGS84] National Imagery and Mapping Agency, "Department of
Defense World Geodetic System 1984, Third Edition", 1984.
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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 "2.1.1.
Position"):
{
"type": "LineString",
"coordinates": [
[100.0, 0.0],
[101.0, 1.0]
]
}
A.3. Polygons
Coordinates of a Polygon are an array of LinearRing (cf. "2.1.6
Polygon") 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],
[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]
],
[
[100.8, 0.8],
[100.8, 0.2],
[100.2, 0.2],
[100.2, 0.8],
[100.8, 0.8]
]
]
}
With hole crossing dateline:
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{
"type": "Polygon",
"coordinates": [
[
[-170.0, 10.0],
[170.0, 10.0],
[170.0, -10.0],
[-170.0, -10.0],
[-170.0, 10.0]
],
[
[175.0, 5.0],
[-175.0, 5.0],
[-175.0, -5.0],
[175.0, -5.0],
[175.0, 5.0]
]
]
}
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],
[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]
]
]
]
}
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. Contributors
The GeoJSON format is the product of discussion on the GeoJSON
mailing list: http://lists.geojson.org/listinfo.cgi/geojson-
geojson.org.
Comments are solicited and should be addressed to the GeoJSON mailing
list at geojson@lists.geojson.org or to the GeoJSON issue tracker at
https://github.com/geojson/draft-geojson/issues.
Authors' Addresses
H. Butler
Hobu Inc.
M. Daly
Cadcorp
A. Doyle
MIT
S. Gillies
Mapbox Inc.
Email: sean.gillies@gmail.com
URI: http://sgillies.net
T. Schaub
OpenGeo
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S. Drees
Rheinaustr. 62
Bonn 53225
DE
Email: stefan@drees.name
URI: http://sdre.es/
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