TopoJSON

.topojson

Supported

TopoJSON is a GeoJSON extension developed by Mike Bostock that encodes topology to eliminate redundant shared boundaries. Unlike GeoJSON where each polygon independently stores all vertices, TopoJSON uses arcs to share common boundaries between adjacent features, reducing file sizes by over 80%. TopoJSON is particularly suited for rendering large numbers of adjacent areas such as administrative district maps.

Specifications

Standard: GitHub

MIME: application/json, application/topo+json

Key Features

Topology encoding eliminates redundant vertices, file size 80%+ smaller than GeoJSON
Preserves topological relationships between features for adjacency analysis
Can be easily converted back to GeoJSON for rendering

Advantages

Dramatically reduces network transfer and storage requirements
Topological relationships support efficient geometric operations

Limitations

Smaller ecosystem, tool support not as widespread as GeoJSON
Requires additional decoding step for map rendering

Common Use Cases

Efficient rendering of large adjacent areas like administrative districts in web maps
GIS applications requiring topology analysis (adjacency, containment)