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Convert FlatGeobuf to GML Online — Free GIS Converter

Convert FlatGeobuf (.fgb) files to GML for OGC-compliant submissions, EU INSPIRE data exchange, and WFS services — automatic CRS detection and browser-based conversion.

Updated May 2026

Modern GIS pipelines often store data in FlatGeobuf for performance, but regulatory submissions, government data portals, and OGC web services require GML — convert your .fgb file to a standards-compliant .gml file with geodata.plus.

Why convert FlatGeobuf to GML?

FlatGeobuf is designed for speed and cloud-native access patterns, but it is rarely accepted by government data submission systems, national spatial data infrastructures, or OGC Web Feature Services. These systems mandate GML because of its explicit CRS declarations, complex feature typing, and long-standing support in geospatial standards bodies. Organizations that use FlatGeobuf as an internal storage format often need to produce GML exports for INSPIRE-compliant submissions, land registry filings, or infrastructure regulatory reports.

GML also enables precise data typing and schema validation that is important in contexts where data quality and interoperability must be formally demonstrated.

Why use geodata.plus

  • Free tier — convert up to 3 files per month at no cost, no credit card required
  • Automatic CRS detection — reads the CRS from the FlatGeobuf header and encodes it as a proper EPSG URN in the GML output
  • Optional reprojection — reproject to any target EPSG (e.g., ETRS89 for EU INSPIRE submissions) before download
  • Browser-based — no QGIS, GDAL, or GML tooling needed; works on any modern browser
  • Encrypted transfer — all uploads use TLS; files are stored temporarily in Cloudflare R2 and automatically deleted on schedule
  • Auto-deleted output — output files are automatically deleted after 2 days (free tier) and 7 days (Pro); no manual cleanup needed

How it works

  1. Upload your FlatGeobuf file (.fgb) using the widget above
  2. geodata.plus reads the CRS, geometry type, and attribute schema from the FlatGeobuf header
  3. Select GML as the output format; optionally reproject to the target EPSG required by the receiving system
  4. Download your .gml file with proper srsName declarations ready for OGC-compliant submission

FlatGeobuf format

FlatGeobuf is a binary, row-oriented vector format built on the FlatBuffers serialization library. It embeds a Hilbert R-tree spatial index at the start of the file for fast HTTP range request queries. The CRS is stored in the file header as an EPSG code. FlatGeobuf supports all OGC geometry types and typed attribute columns. It is the preferred format for serving large vector datasets from cloud storage without a tile server.

| Property | Value | |---|---| | Extension | .fgb | | Type | Vector, single file (binary) | | Coordinate system | Any CRS (stored in header) | | Geometry types | Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, GeometryCollection | | Common software | GDAL, QGIS, Mapbox, cloud-native GIS, web APIs |

GML format

GML (Geography Markup Language) is an XML grammar standardized by the OGC for representing and transporting geographic features. It encodes the CRS as an EPSG URN in the srsName attribute of geometry elements, supports complex feature schemas with typed properties, and is the backbone of OGC WFS services and the EU INSPIRE data exchange framework. GML is verbose but formally unambiguous and directly parseable by ArcGIS, QGIS, and GDAL.

| Property | Value | |---|---| | Extension | .gml | | Type | Vector, single file (XML) | | Coordinate system | Any CRS (EPSG URN encoded in the file) | | Geometry types | Point, LineString, Polygon, MultiGeometry, Curve, Surface | | Common software | ArcGIS, QGIS, GDAL, government portals, EU INSPIRE, WFS services |

Frequently asked questions

Which GML version is output and why does it matter?

geodata.plus outputs GML 3.2.1 by default, which is mandated by the EU INSPIRE Directive and is the version expected by most modern government submission systems. GML 2.1.2 output is available for legacy WFS services that have not been updated to support GML 3. Specify your version requirement before starting the conversion if your target system needs a specific version.

FlatGeobuf supports typed columns — are those data types preserved in GML?

Yes. FlatGeobuf's typed attribute schema (integers, floats, strings, booleans, dates) is mapped to corresponding GML property types. String values are encoded as xs:string, integers as xs:integer, floats as xs:double, and dates as xs:date. This preserves type information for downstream schema validation.

My FlatGeobuf file contains polygon geometries — will they be output as GML Surface or Polygon?

geodata.plus outputs simple polygons as GML <gml:Polygon> elements and multi-polygons as <gml:MultiSurface> elements. If your submission requires a specific GML geometry encoding (e.g., gml:Surface with gml:PolygonPatch for INSPIRE address themes), contact us for a customized conversion profile.

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