| Keyhole Markup Language | |
|---|---|
 | |
| Filename extensions | .kml,.kmz |
| Internet media type |
|
| Developed by | Keyhole, Inc.,Google |
| Type of format | GIS file format |
| Extended from | XML |
Keyhole Markup Language (KML) is anXML notation for expressing geographic annotation and visualization within two-dimensional maps and three-dimensionalEarth browsers. KML was developed for use withGoogle Earth, which was originally named Keyhole Earth Viewer. It was created byKeyhole, Inc, which was acquired byGoogle in 2004. KML became an international standard of theOpen Geospatial Consortium in 2008.[1][2] Google Earth was the first program able to view and graphically edit KML files, but KML support is now available in manyGIS software applications, such asMarble,[3]QGIS,[4] andArcGIS.[5]
The KML file specifies a set of features (place marks, images, polygons, 3D models, textual descriptions, etc.) that can be displayed on maps ingeospatial software implementing the KML encoding. Every place has alongitude and alatitude. Other data can make a view more specific, such as tilt, heading, or altitude, which together define a "camera view" along with a timestamp or timespan. KML shares some of the same structural grammar asGeography Markup Language (GML). Some KML information cannot be viewed in Google Maps or Mobile.[6]
KML files are very often distributed asKMZ files, which arezipped KML files with a .kmz extension. The contents of a KMZ file are a single root KML document and optionally any overlays, images, icons, andCOLLADA 3D models referenced in the KML including network-linked KML files. The root KML document by convention is a file named "doc.kml" at the root directory level, which is the file loaded upon opening. By convention the root KML document is at root level and referenced files are in subdirectories (e.g. images for overlay).[7]
An example KML document is:
<?xml version="1.0" encoding="UTF-8"?><kmlxmlns="http://www.opengis.net/kml/2.2"><Document><Placemark><name>NewYorkCity</name><description>NewYorkCity</description><Point><coordinates>-74.006393,40.714172,0</coordinates></Point></Placemark></Document></kml>
TheMIME type associated with KML isapplication/vnd.google-earth.kml+xml; the MIME type associated with KMZ isapplication/vnd.google-earth.kmz.
For its reference system, KML uses 3D geographic coordinates: longitude, latitude, and altitude, in that order, with negative values for west, south, and below mean sea level. The longitude/latitude components (decimal degrees) are as defined by theWorld Geodetic System of 1984 (WGS84). Altitude, the vertical component, is measured in meters from theWGS84 EGM96 Geoid vertical datum. If altitude is omitted from a coordinate string, e.g. (-77.03647, 38.89763) then the default value of 0 (approximately sea level) is assumed for the altitude component, i.e. (-77.03647, 38.89763, 0).
A formal definition of the coordinate reference system (encoded as GML) used by KML is contained in the OGC KML 2.2 Specification. This definition references well-knownEPSGCRS components.[8]
The KML 2.2 specification was submitted to the Open Geospatial Consortium to assure its status as an open standard for allgeobrowsers. In November 2007 a new KML 2.2 Standards Working Group was established within OGC to formalize KML 2.2 as an OGC standard. Comments were sought on the proposed standard until January 4, 2008,[9] and it became an official OGC standard on April 14, 2008.[10]
The OGC KML Standards Working Group finished working on change requests to KML 2.2 and incorporated accepted changes into the KML 2.3 standard.[11]The official OGC KML 2.3 standard was published on August 4, 2015.[12]
Authority control databases: National |
|---|
