KML (Keyhole Markup Language)

KML is a language for describing geographic data, invented for Google Earth and later adopted as an OGC standard. The file is text: inside are placemarks, lines, outlines, their styles and labels. It opens with a double click in Google Earth and attaches in Google My Maps, QGIS and ArcGIS.

OpenStreetMap maps are exported to KML when the result has to be shown to another person: a client, colleagues, students. The features land on the globe, a click shows their properties, and the file itself can be sent by email — the recipient needs no GIS, Google Earth is enough.

In the file all the layers are laid out in folders named after the layers, each feature keeps its OSM tags in the ExtendedData block, and lines and fills get a color and a width. Coordinates are WGS84, as the specification requires. Roads, water and greenery lie on the ground surface, while buildings are extruded into volume: height is taken from the height tag, or computed from the floor count in building:levels at 3.5 meters per floor, and if neither is present the house gets six meters.

In Google Earth such an export looks like a three-dimensional city right away. If you do not need the volume, switch the buildings layer off in the tree on the left. For sending by email KMZ is handier — the same document in compressed form.