TopoJSON to JSON-FG

TopoJSON to JSON-FG Converter

TopoJSON is a topology-aware JSON format that reduces redundancy by storing shared geometry arcs once instead of repeating them for every feature. Convert it to JSON-FG locally in your browser, inspect the map preview first, and export the generated files without uploading anything to a server.

Source Format Guide

What is TopoJSON?

TopoJSON is a topology-aware JSON format that reduces redundancy by storing shared geometry arcs once instead of repeating them for every feature.

TopoJSON is especially valuable for web-delivered boundary and polygon datasets where neighboring features share edges and repeated coordinates would otherwise bloat the file.

Its topology model makes it efficient for delivery, but many editing and GIS workflows still prefer to convert TopoJSON into ordinary feature collections before working with it.

Common Workflows

Common use cases

Country, state, county, district, or service-area boundary layers on the web.
Thematic maps where many adjacent polygons share borders.
Preprocessed browser assets that need smaller download sizes than plain GeoJSON.

Ecosystem

Where you will encounter it

Browser map assets and thematic web cartography.
Boundary-heavy data publishing workflows.
Developer toolchains that care about compact JSON payloads.

Strengths

Why teams choose TopoJSON

Topology-aware encoding can be smaller than equivalent GeoJSON for shared-edge data.
Good fit for compact web delivery of boundary layers.
Still JSON-based, which keeps it approachable in developer tooling.

Limitations

Where TopoJSON gets awkward

Topology adds complexity that many desktop GIS editing workflows do not want directly.
Not every conversion target writes TopoJSON, so it often acts as an input rather than a round-trip editing format.
Teams commonly need to expand it back into ordinary features before analysis or manual QA.

File Structure

Common file extensions and sidecar files

.topojson

Common extension used for TopoJSON documents containing shared arcs and objects.

.json

Generic JSON extension sometimes used when a pipeline does not preserve the more explicit .topojson suffix.

arcs / objects

Core TopoJSON structures that store shared geometry and feature collections separately.

Conversion Rationale

Why convert TopoJSON to JSON-FG?

Teams commonly convert TopoJSON into JSON-FG when they need a JSON workflow with more geospatial semantics than classic GeoJSON.

Teams convert TopoJSON when they need ordinary features for editing, export, or compatibility with tools that do not understand topology-aware JSON.
They also convert into TopoJSON when web delivery size matters and the source dataset contains many shared polygon boundaries.
JSON-FG can preserve feature typing, richer CRS handling, and newer geospatial JSON patterns.
It is a useful target when you want JSON ergonomics without being limited to classic GeoJSON assumptions.

FAQ

Frequently asked questions about TopoJSON

Why is TopoJSON often smaller than GeoJSON?

Shared edges are stored once and reused across features, which avoids repeating the same coordinates again and again.

Is TopoJSON good for editing?

It is usually more convenient to convert it to a flat feature format first, because most editing tools expect ordinary features instead of shared topology structures.

When should I publish TopoJSON?

Publish TopoJSON when the data is boundary-heavy, web-facing, and benefits from compact JSON delivery.