KML

{{Article
 * Author=Andrew Keske
 * Editor=Chris Maderia
 * BoK Topic=GD12-4
 * 311 Week=7
 * Tags=KML, web, Google, geographic markup language
 * Content=KML (Keyhole Markup Language) is an XML-scheme language that is designed to express geographic data on the internet. It was created to store points, lines, and polygons and have them displayed on Google Earth, Google Maps and other applications.

KML files are similar to the standard of HTML and XML. Like HTML files, KML files work with tags and attributes and interact with a web browser in a manner similar to HTML. Thus, Google Earth which was developed to view KML files is essentially acting like a web browser for many different KML files. Google Earth was the first viewer for KML files.

An OGC Standard
Google submitted KML to the Open Geospatial Consortium (OGC) with the following goal: KML Version 2.2 to be adopted as an OGC implementation standard. Google is continually working to have the KML files become more integrated and a greater standard to match other standards such as GML (Geography Markup Language), WFS (Web Feature Service) and WMS (Web Map Service). To do so there are four objectives that have been developed: "That there be one international standard language for expressing geographic annotation and visualization on existing or future web-based online and mobile maps (2d) and earth browsers (3d). That KML be aligned with international best practices and standards, thereby enabling greater uptake and interoperability of earth browser implementations. That the OGC and Google will work collaboratively to ensure that the KML implementer community is properly engaged in the process and that the KML community is kept informed of progress and issues. That the OGC process will be used to ensure proper life-cycle management of the KML Standard, including such issues as backwards compatibility." 

Structure
A placemark is a common feature used in Google Earth and on Google Maps. It denotes a location on the earth's surface using a pushpin icon. The following is an example of the basic code used to create a placemark within a KML document:

 Simple placemark Attached to the ground. Intelligently places itself at the height of the underlying terrain.  -122.0822035425683,37.42228990140251,0     

As can be seen above in the tag, KML uses 3D geographic coordinates; they are always listed in the order of longitude, latitude, and altitude. Each of these components uses the World Geodetic System of 1984 (WGS84) datum. If altitude is omitted, then the default value is 0 (or sea level). Other features that can be created for display using KML code include: paths, polygons, ground overlays, and screen overlays. Each of these features can be displayed in applications such as Google Earth/Maps/Mobile, NASA WorldWind, ESRI ArcGIS Explorer, Adobe Photoshop, and AutoCAD (all of which are capable of displaying KML). }}