What is a KMZ file and why do I need one? A KMZ is a zipped file containing one or compressed KML files. KMZ is a file extension for a placemark file used by Google Earth. You can open a KMZ file in Google Maps by saving the KMZ file to an online location and then typing the URL in the Google Maps search box. However, for this tutorial, you will need Earth for Desktop installed on your computer. Keyhole Markup Language (KML) is an XML notation for expressing geographic annotation and visualization within two-dimensional maps and three-dimensional Earth browsers.