GeoJSON

From Infogalactic: the planetary knowledge core
Jump to: navigation, search
GeoJSON
Filename extensions .json, .geojson
Internet media type application/vnd.geo+json
Type of format GIS file format
Extended from JSON
Open format? yes
Website geojson.org

GeoJSON[1] is an open standard format designed for representing simple geographical features, along with their non-spatial attributes, based on JavaScript Object Notation.[2][3]

The features include points (therefore addresses and locations), line strings (therefore streets, highways and boundaries), polygons (countries, provinces, tracts of land), and multi-part collections of these types. GeoJSON features need not represent entities of the physical world only; mobile routing and navigation apps, for example, might describe their service coverage using GeoJSON.[4]

The GeoJSON format differs from other GIS standards in that it was written and is maintained not by a formal standards organization, but by an Internet working group of developers.[5]

A notable offspring of GeoJSON is TopoJSON, an extension of GeoJSON that encodes geospatial topology and that typically provides smaller file sizes.

History

The GeoJSON format working group and discussion were begun in March 2007[6] and the format specification was finalized in June 2008.

Example

{ "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"}
           }
         }
       ]
     }

Geometries

Geometry primitives
Type Examples
Point File:SFA Point.svg 
{ "type": "Point", 
    "coordinates": [30, 10]
}
LineString File:SFA LineString.svg 
{ "type": "LineString", 
    "coordinates": [
        [30, 10], [10, 30], [40, 40]
    ]
}
Polygon File:SFA Polygon.svg 
{ "type": "Polygon", 
    "coordinates": [
        [[30, 10], [40, 40], [20, 40], [10, 20], [30, 10]]
    ]
}
File:SFA Polygon with hole.svg 
{ "type": "Polygon", 
    "coordinates": [
        [[35, 10], [45, 45], [15, 40], [10, 20], [35, 10]], 
        [[20, 30], [35, 35], [30, 20], [20, 30]]
    ]
}
Multipart geometries
Type Examples
MultiPoint File:SFA MultiPoint.svg 
{ "type": "MultiPoint", 
    "coordinates": [
        [10, 40], [40, 30], [20, 20], [30, 10]
    ]
}
MultiLineString File:SFA MultiLineString.svg 
{ "type": "MultiLineString", 
    "coordinates": [
        [[10, 10], [20, 20], [10, 40]], 
        [[40, 40], [30, 30], [40, 20], [30, 10]]
    ]
}
MultiPolygon File:SFA MultiPolygon.svg 
{ "type": "MultiPolygon", 
    "coordinates": [
        [
            [[30, 20], [45, 40], [10, 40], [30, 20]]
        ], 
        [
            [[15, 5], [40, 10], [10, 20], [5, 10], [15, 5]]
        ]
    ]
}
File:SFA MultiPolygon with hole.svg 
{ "type": "MultiPolygon", 
    "coordinates": [
        [
            [[40, 40], [20, 45], [45, 30], [40, 40]]
        ], 
        [
            [[20, 35], [10, 30], [10, 10], [30, 5], [45, 20], [20, 35]], 
            [[30, 20], [20, 15], [20, 25], [30, 20]]
        ]
    ]
}

Supported software

GeoJSON is supported by numerous mapping and GIS software packages, including OpenLayers,[7] Leaflet, MapServer,[8] Geoforge software,[9] GeoServer,[10] GeoDjango,[11] GDAL,[12] Safe Software FME,[13] and CartoDB.[14] It is also possible to use GeoJSON with PostGIS[15] and Mapnik,[16] both of which handle the format via the GDAL OGR conversion library. Bing Maps, Yahoo! and Google also support GeoJSON in their API services.

The Google Maps Javascript API v3 directly supports the integration of GeoJSON data layers [17] as of March 19, 2014.[18]

GitHub also supports GeoJSON rendering[19] and Potrace GeoJSON export.

TopoJSON

TopoJSON is an extension of GeoJSON that encodes topology. Rather than representing geometries discretely, geometries in TopoJSON files are stitched together from shared line segments called arcs.[20] Arcs are sequences of points, while line strings and polygons are defined as sequences of arcs. Each arc is defined only once, but can be referenced several times by different shapes, thus reducing redundancy and decreasing the file size.[21] In addition, TopoJSON facilitates applications that use topology, such as topology-preserving shape simplification, automatic map coloring, and cartograms.

A reference implementation of the TopoJSON specification is available as a command-line tool to encode TopoJSON from GeoJSON (or ESRI Shapefiles) and a client side JavaScript library to decode TopoJSON back to GeoJSON again. TopoJSON is also supported by the popular OGR tool as of version 1.11[22] and PostGIS as of version 2.1.0.[23]

TopoJSON Schema

Given a GIS shape near coordinates latitude 0° en longitude 0° a simple but valid and complete topojson file containing all metadata, Polygon, LineString, Point elements, arcs and properties is defined as follows:

File:Topojson shapes-en.svg
400px
{
  "type":"Topology",
  "transform":{
    "scale": [1,1],
    "translate": [0,0]
  },
  "objects":{ 
    "two-squares":{
      "type": "GeometryCollection",
      "geometries":[
        {"type": "Polygon", "arcs":[[0,1]],"properties": {"name": "Left_Polygon" }},
        {"type": "Polygon", "arcs":[[2,-1]],"properties": {"name": "Right_Polygon" }}
      ]
    },
    "one-line": {
      "type":"GeometryCollection",
      "geometries":[
        {"type": "LineString", "arcs": [3],"properties":{"name":"Under_LineString"}}
      ]
    },
    "two-places":{
      "type":"GeometryCollection",
      "geometries":[
        {"type":"Point","coordinates":[0,0],"properties":{"name":"Origine_Point"}},
        {"type":"Point","coordinates":[0,-1],"properties":{"name":"Under_Point"}}
      ]
    }
  },
  "arcs": [
    [[1,2],[0,-2]],
    [[1,0],[-1,0],[0,2],[1,0]],
    [[1,2],[1,0],[0,-2],[-1,0]],
    [[0,-1],[2,0]]
  ]
}

References

  1. ↑ The GeoJSON Format Specification
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ iOS Location and Maps Programming Guide
  5. ↑ The GeoJSON Discussion List
  6. ↑ March 2007 Archives by thread
  7. ↑ http://openlayers.org/dev/examples/vector-formats.html
  8. ↑ http://mapserver.org/output/template_output.html
  9. ↑ http://leafletjs.com/reference.html#geojson
  10. ↑ http://svn.codehaus.org/geoserver/tags/2.0.0-alpha1/geoserver/release/README.txt
  11. ↑ http://geodjango.org
  12. ↑ http://gdal.org/ogr/drv_geojson.html
  13. ↑ http://www.safe.com/reader_writerPDF/geojson.pdf
  14. ↑ http://developers.cartodb.com/documentation/cartodb-js.html
  15. ↑ http://pugs.postgresql.org/files/Introduction_to_PostGIS_v1.0.pdf
  16. ↑ http://svn.mapnik.org/tags/release-0.6.0/docs/api_docs/python/mapnik-module.html
  17. ↑ https://developers.google.com/maps/documentation/javascript/examples/layer-data-simple
  18. ↑ http://googledevelopers.blogspot.com/2014/03/maps-made-easier-geojson-in-javascript.html
  19. ↑ https://github.com/blog/1528-there-s-a-map-for-that
  20. ↑ https://github.com/topojson/topojson-specification
  21. ↑ https://github.com/mbostock/topojson/wiki
  22. ↑ GDAL/OGR 1.11.0 Release Notes
  23. ↑ PostGIS AsTopoJSON

Sources

Retrieved from "https://infogalactic.com/w/index.php?title=GeoJSON&oldid=1918376"