A TopoJSON file format is a geoJSON format extension that encodes geospatial topology. TopoJSON files contain both attribute data and geospatial data (arcs). Arcs — or sequences of points which can then be used to define line strings and polygons — can be referenced numerous times by different shapes within the file, and therefore greatly decrease data redundancy and the overall size of TopoJSON files. This format's use of arcs set the TopoJSON apart from other GIS formats. This format is often used by software such as Microsoft PowerBI.
A complete TopoJSON dataset contains the following specifications when exporting from Spotzi: