<div dir="ltr">The meaning of the coordinate values depends on the coordinate reference system (CRS) the GeoJSON file uses.<div><br></div><div style>The default CRS is WGS84 (EPSG:4326), where the values do represent longitude, latitude, and optional altitude.</div>
<div style><br></div><div style>If you specify a different CRS in the GeoJSON file, then the coordinate values are easting, northing, and again optional altitude. The meaning of the easting and northing depends on the CRS. I believe altitude is in meters in all cases; someone correct me if I'm wrong.</div>
<div style><br></div><div style>As an example, my PolyGonzo library accepts GeoJSON in either the default WGS84, or alternatively in Spherical Mercator (EPSG:3857) coordinates, also known as Google Mercator. These are coordinates in "meters" on the projected Spherical Mercator plane. If you use this in the GeoJSON, it allows slightly faster display of the polygons because it only takes a single multiplication to convert each coordinate to a pixel location instead of a sequence of trigonometric operations.</div>
<div style><br></div><div style>Here's an example of GeoJSON using Spherical Mercator coordinates. This file contains the boundary of the District of Columbia, from my Google election results map.</div><div style><br>
</div><div style><div><font face="courier new, monospace"> {</font></div><div><font face="courier new, monospace"> "crs": {</font></div><div><font face="courier new, monospace"> "type": "name",</font></div>
<div><font face="courier new, monospace"> "properties": {</font></div><div><font face="courier new, monospace"> "name": "urn:ogc:def:crs:EPSG::3857"</font></div><div>
<font face="courier new, monospace"> }</font></div><div><font face="courier new, monospace"> },</font></div><div><font face="courier new, monospace"> "features": [</font></div><div><font face="courier new, monospace"> {</font></div>
<div><font face="courier new, monospace"> "name": "District of Columbia",</font></div><div><font face="courier new, monospace"> "geometry": {</font></div><div><font face="courier new, monospace"> "type": "MultiPolygon",</font></div>
<div><font face="courier new, monospace"> "coordinates": [</font></div><div><font face="courier new, monospace"> [</font></div><div><font face="courier new, monospace"> [</font></div>
<div><font face="courier new, monospace"> [ -8576165, 4720971 ],</font></div><div><font face="courier new, monospace"> [ -8571687, 4716527 ],</font></div><div>
<font face="courier new, monospace"> [ -8561515, 4706329 ],</font></div><div><font face="courier new, monospace"> [ -8575898, 4691851 ],</font></div><div><font face="courier new, monospace"> [ -8575586, 4695194 ],</font></div>
<div><font face="courier new, monospace"> [ -8576553, 4698721 ],</font></div><div><font face="courier new, monospace"> [ -8575252, 4699023 ],</font></div><div>
<font face="courier new, monospace"> [ -8575129, 4700281 ],</font></div><div><font face="courier new, monospace"> [ -8576120, 4703241 ],</font></div><div><font face="courier new, monospace"> [ -8576655, 4703812 ],</font></div>
<div><font face="courier new, monospace"> [ -8577066, 4703169 ],</font></div><div><font face="courier new, monospace"> [ -8579404, 4707459 ],</font></div><div>
<font face="courier new, monospace"> [ -8582844, 4708927 ],</font></div><div><font face="courier new, monospace"> [ -8584948, 4712267 ],</font></div><div><font face="courier new, monospace"> [ -8576165, 4720971 ]</font></div>
<div><font face="courier new, monospace"> ]</font></div><div><font face="courier new, monospace"> ]</font></div><div><font face="courier new, monospace"> ]</font></div>
<div><font face="courier new, monospace"> },</font></div><div><span style="font-family:'courier new',monospace"> "centroid": [ -8573379, 4708026 ],</span><br></div><div><font face="courier new, monospace"> "bbox": [ -8584948, 4691851, -8561515, 4720971 ],</font></div>
<div><font face="courier new, monospace"> "type": "Feature",</font></div><div><font face="courier new, monospace"> "id": "0500000US11001"</font></div>
<div>
<font face="courier new, monospace"> }</font></div><div><font face="courier new, monospace"> ],</font></div><div><font face="courier new, monospace"> "table": "carto2010.county_512",</font></div>
<div><font face="courier new, monospace"> "center": [ -8573231, 4706411 ],</font></div><div><font face="courier new, monospace"> "type": "FeatureCollection",</font></div><div><font face="courier new, monospace"> "id": "11",</font></div>
<div><font face="courier new, monospace"> "bbox": [ -8584948, 4691851, -8561515, 4720971 ],</font></div><div><font face="courier new, monospace"> "name": "District of Columbia"</font></div>
<div><font face="courier new, monospace"> }</font></div><div><br></div></div><div style><br></div><div style>Further reading:</div><div style><br></div><div style><a href="http://www.geojson.org/geojson-spec.html#positions">http://www.geojson.org/geojson-spec.html#positions</a><br>
</div><div style><br></div><div style><a href="http://www.geojson.org/geojson-spec.html#coordinate-reference-system-objects">http://www.geojson.org/geojson-spec.html#coordinate-reference-system-objects</a><br></div><div style>
<br></div><div style><a href="http://en.wikipedia.org/wiki/World_Geodetic_System">http://en.wikipedia.org/wiki/World_Geodetic_System</a><br></div><div style><br></div><div style><a href="http://docs.openlayers.org/library/spherical_mercator.html">http://docs.openlayers.org/library/spherical_mercator.html</a><br>
</div><div style><br></div><div style><a href="https://code.google.com/p/polygonzo/">https://code.google.com/p/polygonzo/</a><br></div><div style><br></div><div style>-Mike</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">
On Wed, Mar 6, 2013 at 7:49 AM, Francis Galiegue <span dir="ltr"><<a href="mailto:fgaliegue@gmail.com" target="_blank">fgaliegue@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello,<br>
<br>
First, a short announce to say that the schemas for GeoJSON have<br>
moved. Their new home is:<br>
<br>
<a href="https://github.com/fge/sample-json-schemas/tree/master/geojson" target="_blank">https://github.com/fge/sample-json-schemas/tree/master/geojson</a><br>
<br>
And then I have a question about valid numeric values in points etc. I<br>
guess those are latitude or longitude coordinates?<br>
<br>
--<br>
Francis Galiegue, <a href="mailto:fgaliegue@gmail.com">fgaliegue@gmail.com</a><br>
JSON Schema in Java: <a href="http://json-schema-validator.herokuapp.com" target="_blank">http://json-schema-validator.herokuapp.com</a><br>
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</blockquote></div><br></div>