KML vs GeoJSON

KML and GeoJSON can both represent geographic features, but they were designed around different jobs.

KML is an XML language focused on geographic visualisation, annotation, camera behaviour, and presentation in earth browsers. GeoJSON is a JSON format focused on geographic features and properties, with especially strong integration in web APIs and JavaScript mapping libraries.

If you are publishing an interactive overlay with KML-specific presentation, tours, ground overlays, or Google Earth-style behaviour, KML may be the natural format. If you are exchanging feature data with a web application or API, GeoJSON is usually simpler.

Different design centres

The OGC describes KML as a language for geographic visualisation: what to show in an earth browser and how to show it. Its model includes placemarks, styles, folders, overlays, views, and navigation concepts.

GeoJSON, standardised in RFC 7946, has a narrower core. It represents geometries, Features, FeatureCollections, and properties using ordinary JSON structures.

That difference explains much of their behaviour.

KML can therefore carry presentation instructions that do not have a direct GeoJSON equivalent, whereas GeoJSON is easier to treat as application data independent of one visualisation environment.

Geometry support overlaps, but the containers differ

Both formats support familiar vector geometries such as points, lines, and polygons.

KML places them inside XML elements such as Placemark, while GeoJSON represents them through JSON objects with a type and coordinates member.

A GeoJSON feature might look conceptually like:

{
  "type": "Feature",
  "geometry": {"type": "Point", "coordinates": [9.7, 4.05]},
  "properties": {"name": "Example"}
}

The equivalent KML is more verbose XML but can participate in KML-specific styling and presentation structures.

Coordinate-reference behaviour is different

RFC 7946 fixes GeoJSON's interoperable coordinate reference system to WGS 84 longitude/latitude coordinates in the CRS84 axis order. The old practice of embedding arbitrary CRS objects is not part of modern RFC 7946 GeoJSON.

KML likewise uses longitude/latitude coordinates associated with WGS 84 for its geographic model, so neither format should be used as a generic container for arbitrary projected coordinates without explicit conversion into the format's expected coordinate model.

Styling is a major KML strength

KML can encode styles, icons, labels, line/polygon presentation, balloons, camera views, and other display-oriented behaviour.

GeoJSON, by contrast, deliberately does not standardise map styling. A GeoJSON file can contain properties used by an application to choose colours or symbols, but the styling rules belong to the renderer or a separate style specification.

This makes GeoJSON portable as data, but it also means converting KML to GeoJSON can discard presentation semantics unless those are stored separately.

GeoJSON fits web application data more naturally

JSON is a native data structure in JavaScript environments, and GeoJSON is supported by many browser mapping libraries and geospatial APIs.

For modest datasets, it is easy to inspect, debug, generate, and send over HTTP, and its simplicity also makes it useful as an interchange format between services. That simplicity has a cost, however: large GeoJSON files can become expensive to download, parse, and render in browsers. Why Large GeoJSON Files Make Web Maps Slow explains why larger web maps often move to tiled delivery.

Conversion can lose more than geometry

A KML-to-GeoJSON conversion may preserve points, lines, polygons, and selected attributes while losing or transforming:

KML styles;
folders and document hierarchy;
camera/view information;
tours;
ground overlays;
network links;
time or altitude semantics that the target tool does not preserve;
application-specific extended data.

The reverse conversion can also be lossy because arbitrary GeoJSON properties and data types do not map perfectly into every KML workflow.

Always validate a representative subset after conversion rather than treating “features imported successfully” as proof of semantic equivalence.

Which should you use?

Choose KML when the deliverable is centred on geographic presentation in KML-aware earth browsers or when KML-specific styling and viewing behaviour matter. Choose GeoJSON when the deliverable is feature data for web applications, APIs, lightweight exchange, or developer workflows where JSON integration is valuable.

For larger analytical datasets, neither may be ideal: GeoPackage or GeoParquet may preserve richer schemas or scale better for processing.

References

OGC KML Standard. Defines KML as an XML language focused on geographic visualisation and earth-browser presentation.
RFC 7946 — The GeoJSON Format. Defines GeoJSON geometries, Features, FeatureCollections, and coordinate conventions.