FlatGeobuf

FlatGeobuf is a modern binary vector format designed for fast streaming reads. A single self-contained file with UTF-8 text encoding, it avoids the companion-file clutter of Shapefile. Its optional embedded spatial index enables efficient bounding-box queries without reading the whole file, making it well-suited to large datasets served over HTTP. It also works well as a general-purpose GIS exchange format.

File extension: .fgb · Read: ✓ · Write: ✓ · Multi-layer: no (one layer per file)

CLI examples

mapshaper buildings.fgb -info
mapshaper buildings.fgb -simplify 5% -o buildings.geojson
mapshaper provinces.shp -o provinces.fgb

Format-specific input options

There are no FlatGeobuf-specific -i options.

Format-specific output options

There are no FlatGeobuf-specific -o options. The format honors the general flags (precision=, gzip, zip, etc.) where they apply.

Practical notes

• Mapshaper reads CRS metadata from the file header when it's encoded as an EPSG code. WKT2-only definitions can't be parsed and produce an "Unable to import WKT2 CRS from FlatGeobuf" warning — the layer comes in without a CRS.
• On output, Mapshaper embeds an EPSG code in the FlatGeobuf header whenever it can derive one from the source: a round-tripped FlatGeobuf or GeoPackage CRS, an epsg:NNNN string passed to -proj, an AUTHORITY["EPSG", N] clause in a Shapefile .prj, or any encoding of WGS-84 or Web Mercator (which covers most GeoJSON, CSV-with-lat/lon and -proj wgs84/-proj webmercator outputs).
• Mapshaper cannot yet convert an arbitrary proj4 definition (such as a custom Albers projection set with -proj +proj=aea ...) to an EPSG code. In that case the file is written with no CRS in the header and a warning is printed: "Wrote foo.fgb without a CRS in the FlatGeobuf header...". Re-run the file through ogr2ogr if you need the CRS embedded for downstream tools.
• Mapshaper does not write the optional packed R-tree spatial index, and it doesn't use the index for selective reads of indexed input either — the whole file is read into memory. If you need an indexed .fgb for HTTP range-request reads, build it with ogr2ogr or the flatgeobuf CLI.

External resources

• flatgeobuf.org — project home with spec links and language bindings.
• Kicking the Tires: FlatGeobuf — an independent practical writeup with benchmarks against Shapefile, GeoJSON and GeoPackage.
• Bryce Mecum: Flatgeobuf — a hands-on exploration of streaming reads in the browser, including a worth-knowing gotcha about the spatial index sitting at the front of the file.
• Cloud-Native Geospatial Formats Guide: FlatGeobuf — how the format fits into modern cloud-storage workflows.
• FlatGeobuf reading and writing in Mapshaper is built on the official flatgeobuf JavaScript library, which provides the FlatBuffers schema, header parsing and feature serialisation primitives.