KML viewer

KML stands for Keyhole Markup Language. Keyhole was a small company making satellite-imagery software, bought by Google in 2004; the product became Google Earth and the file format kept the old name. It went to the Open Geospatial Consortium as a standard in 2008, and version 2.2 is still what almost everything writes.

Underneath it’s XML, so it’s verbose, readable in a text editor and roughly ten times the size of the same data as GeoJSON. The central idea is the Placemark: a thing with a name, a description and a geometry. Google Earth, Google My Maps, Garmin BaseCamp, ArcGIS and most GIS packages will hand you one. If someone emailed you a map and it isn’t a PDF, there’s a fair chance it’s this.

The format carries far more than geometry: styles, icons, balloon HTML, overlays draped on the terrain, 3D models, time animation. That richness is why a KML can look spectacular in Google Earth and fairly plain anywhere else.

This is a geometry viewer with an editor attached, so it reads the shapes and their names and ignores the presentation. Worth knowing precisely which is which before you rely on it.

The gx:Track one bites hardest. If you recorded a track in Google Earth or a Garmin tool saved its trail as a gx:Track, the file will open and draw nothing, because the points live in Google’s extension rather than in a LineString. Export the same trip as GPX and it opens fine.

Google Earth saves .kmz by default, and Google My Maps often gives you one too, so a lot of people arrive here with the wrong file. A .kmz is a zip archive: a doc.kml plus any custom pin icons and overlay images it needs, bundled so you can email one attachment.

Rename it to .zip, open it, drop the doc.kml from inside. In Google Earth you can also right-click a folder, choose Save Place As and pick KML in the file type dropdown, which skips the zip entirely.

Once the placemarks are on screen, the export buttons in the panel give you four ways out. GeoJSON if it’s going into a web map or a script. GPX if it’s going onto a GPS unit or a watch. CSV if someone wants a spreadsheet, which only works for markers: name, lat, lng, one row each. And KML back out again, if all you wanted was to delete half of it.

A conversion through here is lossy in the way described above. Going to GPX turns polygons into closed lines, since GPX has no concept of an area. GeoJSON gives the cleanest result, because both formats think in the same geometry types.

Circles get special handling in both directions. KML has no circle element, so Google Earth fakes one with a many-sided polygon. A circle exported from here goes out as a polygon too, with its centre and radius written into ExtendedData, which means reopening the file here gives you back a circle you can drag to resize.

Other formats: GeoJSON viewer and GPX viewer.

KML viewers are not a scarce resource. Google’s own My Maps will import one, there are half a dozen free web tools, and Google Earth is right there. For styling, overlays and 3D, Earth wins and it isn’t close.

What this does differently comes down to two things. Nothing is uploaded, which matters when the file is a client site, a survey or anything you’d have to ask a manager about before putting it on someone else’s server. Most of the free converters work by posting your file to a backend.

And the shapes stay editable. Move a misplaced placemark, delete the forty you don’t need, retype a name, add a polygon of your own, then export or share a link that carries the drawing inside the URL. If you only need to look at a file once, any viewer will do. If you need to fix it, doing both in one tab is the point.