Used by Google Earth and other GIS applications, KML is for geographic visualization, including points, lines, polygons, and images.

Keyhole Markup Language (KML) and its compressed variant, KMZ, are data formats used predominantly by geographic information system (GIS) applications such as Google Earth for geographic visualization. This includes the representation of geographical data elements like points, lines, polygons, and images.

KML is an XML-based format with a structure that allows it to be universally accessible and editable, thereby making it ideal for the sharing and distribution of geographical data. It was developed for use with Google Earth, which was originally named 'Keyhole Earth Viewer', thus the name - Keyhole Markup Language. The format was later standardized and is now maintained by the Open Geospatial Consortium (OGC), a non-profit organization providing transparent governance to enhance our world's geospatial interoperability.

The KML file structure contains a series of specific tags, each of which corresponds to a type of geographic data. For instance, the <Placemark> tag designates a geographical feature that can be a point, polygon, or line. The <Point>, <LineString>, and <Polygon> tags define the geometry of the feature, whereas tags such as <Style> and <LineStyle> assign visual properties to the features. Furthermore, KML files can include additional data in the form of text, images, HTML content, and even 3D models, enriching the GIS visualisation without compromising the integrity of the geographical data representation.

KMZ is essentially a compressed version of KML designed to decrease the size of the data file while maintaining all the geospatial information of the original KML file. KMZ files are created using the standard ZIP algorithm and can be uncompressed using any standard ZIP utility. Once uncompressed, they behave like a standard KML file.

In terms of compatibility, while these formats were initially designed for use with Google Earth, their standardization means they are now supported by many GIS and remote sensing applications, including but not limited to Atlas, ESRI's ArcGIS, QGIS, NASA's World Wind, and the Google Maps API.

Despite their universality and flexibility, it's important to note that KML and KMZ have their limitations. They are not intended as a data storage format and do not support attributes in the way that more traditional GIS formats like shapefiles or geodatabases do. As such, they are best suited for the display and transmission of geographic information rather than for carrying out in-depth geospatial analysis.

Overall, KML and KMZ have significantly contributed to the advancement of geographical data sharing, making complex geospatial data more accessible and comprehensible. The simplicity and versatility of these formats have made them ubiquitous across the GIS field. Thus, a profound understanding of KML and KMZ is fundamental to manipulating and leveraging geospatial data effectively in a wide range of GIS applications.

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