Convert KML to FlatGeobuf Online — Free GIS Converter

Convert KML files into FlatGeobuf — the streamable, cloud-native vector format designed for fast HTTP range-request access, high-throughput geospatial APIs, and modern data engineering pipelines.

Why convert KML to FlatGeobuf?

KML is an XML-based format optimized for human readability and Google Earth visualization. It is poorly suited to cloud-native data pipelines: parsing large KML files is slow, the format is not streamable, and HTTP range requests are impossible against its structure. FlatGeobuf solves all of these problems. Built on the FlatBuffers binary serialization library, FlatGeobuf files have a spatial index baked in, support HTTP range requests for partial file retrieval, and can be read at speeds that are orders of magnitude faster than equivalent KML or even GeoJSON.

If you're building a web API that serves spatial data, storing GIS datasets in cloud object storage (S3, GCS, Azure Blob), or ingesting large feature datasets into a GDAL-based pipeline, FlatGeobuf is the right output format.

Why use geodata.plus

• Free tier: convert up to 3 files per month at no cost
• Automatic spatial indexing written into the output FlatGeobuf file
• CRS reprojection support — output in any EPSG code
• Browser-based — no GDAL install or command-line tooling required
• Encrypted upload (TLS); files stored in Cloudflare R2, automatically deleted after 2 days (free) or 7 days (Pro)
• Output is a single binary .fgb file ready for cloud storage or API serving

How it works

1. Upload your KML file to geodata.plus
2. geodata.plus reads all KML features and detects the WGS 84 coordinate system
3. Select FlatGeobuf as the output format; optionally specify a target CRS
4. Download your .fgb file — ready to serve from S3, use with GDAL, or load in Mapbox

KML format

KML is an XML-based vector format produced by Google Earth and other consumer GIS tools. It encodes geometry, styling, and attribute data in a verbose but human-readable structure. KML is always in WGS 84 and is not optimized for programmatic consumption at scale.

| Property | Value | |---|---| | Extension | .kml | | Type | Vector, single-file XML | | Coordinate system | WGS 84 (EPSG:4326) only | | Geometry types | Point, LineString, Polygon, MultiGeometry | | Common software | Google Earth, Google Maps, ArcGIS, QGIS |

FlatGeobuf format

FlatGeobuf is a binary vector format using FlatBuffers encoding with a built-in R-tree spatial index. The format is streamable — a client can issue an HTTP range request against a .fgb file in S3 and retrieve only the features intersecting a bounding box without downloading the whole file. It supports any CRS and all standard vector geometry types. GDAL 3.1+ includes full FlatGeobuf read/write support.

| Property | Value | |---|---| | Extension | .fgb | | Type | Vector, single-file binary | | Coordinate system | Any CRS | | Geometry types | Point, LineString, Polygon, Multi* variants | | Common software | GDAL, Mapbox, cloud-native GIS pipelines, web APIs |

Frequently asked questions

Can I serve a FlatGeobuf file directly from S3 and query it spatially? Yes — this is FlatGeobuf's flagship use case. Because the format supports HTTP range requests, a JavaScript client using the flatgeobuf npm package can query a .fgb file stored in S3 (with appropriate CORS headers) and retrieve only features within a given bounding box, without downloading the entire file. This makes it practical to serve gigabyte-scale datasets from static object storage with no server-side compute.

Is FlatGeobuf readable in QGIS or ArcGIS after converting from KML? QGIS 3.16 and later support FlatGeobuf natively via the GDAL driver — just drag the .fgb file into the layers panel. ArcGIS Pro can read FlatGeobuf through its GDAL integration. If you are on an older ArcGIS Desktop version, you may need to convert the FlatGeobuf to GeoPackage or Shapefile first.

Does FlatGeobuf preserve all KML attribute fields? Yes. All KML <Data> and <ExtendedData> fields are written as feature properties in the FlatGeobuf schema, using their original names (unlike Shapefile, which truncates to 10 characters). The attribute schema is defined in the FlatGeobuf file header, so consuming applications can read field names and types without any external schema file.