KML

KML (Keyhole Markup Language) is an XML-based language for expressing geographic annotation and visualization on maps and 3D globes. It describes features such as points, lines, polygons, raster overlays, and 3D models, together with styling, time data, and metadata.

Developed by Keyhole, Inc. and later adopted by Google, KML has been standardized by the Open Geospatial Consortium (OGC). It is designed to be read by earth browsers and GIS software, enabling easy sharing of geographic information.

Structure: A KML document starts with a kml element in the http://www.opengis.net/kml/2.2 namespace. Inside are containers such as Document and Folder that group features. Core geometry types include Point, LineString, LinearRing, Polygon, and MultiGeometry. Placemark elements tie geometry to properties like name, description, time, and ExtendedData. Coordinates are longitude, latitude, and optional altitude, with altitudeMode options (clampToGround, relativeToGround, absolute). Styles, icons, and style maps control appearance.

Other content includes GroundOverlay, ScreenOverlay, PhotoOverlay, and Model for imagery and 3D content. The gx: extension namespace adds tours, playlists, and tracks. Data can be organized with NetworkLink for remote loading.

Packaging and usage: KML files use the .kml extension; multiple resources can be packaged into a compressed .kmz archive. Applications include sharing geographic data, routes, areas, and timelines across platforms.

Applications and compatibility: KML is widely supported by Google Earth and Google Maps, as well as GIS software such as ArcGIS, QGIS, and NASA WorldWind, making it a common format for interoperable geographic data exchange.