Keyhole Markup Language (KML), referring to the company that developed the format. It can be used to store geographic data which can be visualized using a host of applications such as Google Earth, Esri ArcGIS Explorer, Adobe Photoshop, and AutoCAD. KML is based on XML, using a tag-based structure with nested elements and attributes. KML files are often distributed in KMZ files, which are zipped KML files with a .kmz extension. For its reference system, KML uses longitude, latitude, and altitude coordinates, defined by the World Geodetic System of 1984 (WGS84).