How are KML and KMZ files used in flight simulators?

KML files store geographic points, paths and polygons in XML; KMZ files are compressed KML packages that can also include images and other assets. Across Microsoft Flight Simulator, FSX, Prepar3D and X-Plane, they are mainly route or scenery source data and usually require conversion to a native simulator format.

What is the difference between KML and KMZ?

KML, or Keyhole Markup Language, is a readable text format containing geographic coordinates, labels, styles and geometry. KMZ is a ZIP-compressed package containing a KML document, often named doc.kml, plus associated icons, images or models.

Use KML when converting or troubleshooting data. Use KMZ when the receiving tool explicitly supports it and the project needs bundled assets. Renaming .kmz to .kml does not convert it; extract the archive and use its KML document instead.

Can a flight simulator open KML or KMZ directly?

Usually, a flight simulator cannot use a KML or KMZ file directly as a flight plan or installed scenery package. The file must be imported through a compatible utility, traced in an editor or converted into the simulator's native format.

Import support varies between utilities and simulator generations. A KML file supplied with an add-on may only show coverage or reference points; its presence does not mean that it belongs in the simulator's add-on folder.

Converting a KML path into a flight plan

A KML path can provide the geographic shape of a route, but it is not automatically an aviation flight plan. It may contain coordinates without airway names, navaid identifiers, procedures, runway data or a usable cruise altitude.

1. Inspect the file. Open it in a geographic viewer and identify the intended LineString or sequence of placemarks. Our comparison of Google Earth paths, placemarks and elevation tools for simulator planning explains the useful planning features.
2. Clean the geometry. Remove accidental branches, duplicate points and unrelated polygons. Keep a continuous path where the converter expects one.
3. Convert to the native format. Use an importer or conversion tool that explicitly supports both KML or KMZ and the exact simulator generation. Do not assume a converter for FSX will produce a valid MSFS or X-Plane plan.
4. Rebuild the aviation details. Match coordinates to the simulator's navigation database, then add the correct departure, arrival, approach and cruise altitude. For an operational route rather than a traced path, use these methods for finding real-world flight simulator routes.
5. Validate before flying. Inspect the converted plan on the simulator map for misplaced waypoints, route discontinuities and excessive user-defined points.

KML altitude values deserve special care. Many paths are clamped to the ground or contain zero altitude, while a simulator flight plan expects aviation altitudes. Set and check the cruise and procedure altitudes separately rather than trusting imported values.

How can KML and KMZ files create flight simulator scenery?

KML is useful for defining where scenery features belong, but it does not by itself create buildings, terrain textures or a finished add-on. Its points, lines and polygons must be assigned simulator-specific properties and compiled into a native scenery package.

1. Draw or obtain the geometry. Record the required points, lines and boundaries without including unrelated map data.
2. Check the coordinates. KML normally uses WGS84 longitude, latitude and optional altitude. Confirm that any GIS conversion has not left the data in metres or a projected coordinate system.
3. Assign scenery functions. Decide which polygons represent water, exclusions, land classes or surfaces, and which points place library objects.
4. Convert and compile. Import the geometry into a version-compatible scenery workflow, map it to the simulator's SDK features and build the native package.
5. Test in the simulator. Check shorelines, terrain elevation, object height, package priority and frame-rate impact from overly detailed geometry.

For FSX, the FSX utility for turning KML geometry into scenery components demonstrates the established path-and-polygon workflow. The Sicily lakes scenery built with Google Earth and FSX-KML data is a practical example of geographic outlines becoming compiled water scenery.

Microsoft Flight Simulator and X-Plane use different scenery systems, so the FSX workflow is not directly transferable. KML remains useful as reference geometry, but the final project must use the target simulator's own editor, data structure and package compiler.

Why does a KML or KMZ import fail?

Most KML and KMZ import failures come from incompatible content or malformed geometry rather than damaged coordinates.

• Latitude and longitude are reversed: KML coordinates are ordered longitude, latitude and optional altitude. Swapping them can move scenery thousands of miles or place it outside valid coordinate ranges.
• The KMZ archive is unsupported: Extract its KML file and preserve any relative folders containing images or models. An importer may read the geometry while ignoring bundled assets.
• The altitude mode is wrong: absolute, relativeToGround and clampToGround produce different results. Incorrect interpretation can leave objects underground or floating.
• The polygon is invalid: Self-intersections, duplicate vertices, unclosed boundaries and badly formed holes can stop a scenery compiler or produce inverted areas.
• The geometry is too dense: Thousands of unnecessary vertices increase compilation time, package size and rendering load. Simplify long paths while preserving important bends and boundaries.
• The importer supports only part of KML: Basic points and polygons may work while tours, network links, custom extensions, overlays or embedded models are ignored.
• The route lacks aviation meaning: A geographic line does not automatically identify airways, procedures or database waypoints. Recreate those elements in the native flight planner.
• Source rights are missing: Owning a KML or KMZ file does not grant permission to redistribute the imagery, models or geographic data referenced inside it.

A mistake we see constantly is treating KML as finished simulator content. Keep the original file as editable source data, convert a copy for the intended simulator, and verify the compiled route or scenery in-game before distributing it.