topojson1.2 KB

TopoJSON — Two Parcels Sharing One Arc

Two adjacent parcels that share their common boundary as a single arc: West Field references it as 0 and East Field as ~0, the negative-index form that means traverse it backwards. Storing the boundary once is the whole point of TopoJSON, and it is also where naive decoders produce gaps or slivers.

Geospatial Conversion testing JSON parsing

Preview — first 50 linestopojson

{
  "type": "Topology",
  "objects": {
    "parcels": {
      "type": "GeometryCollection",
      "geometries": [
        {
          "type": "Polygon",
          "id": "P-010",
          "properties": {
            "name": "West Field",
            "areaHa": 1.31
          },
          "arcs": [
            [
              0,
              1
            ]
          ]
        },
        {
          "type": "Polygon",
          "id": "P-011",
          "properties": {
            "name": "East Field",
            "areaHa": 1.31
          },
          "arcs": [
            [
              -1,
              2
            ]
          ]
        }
      ]
    }
  },
  "arcs": [
    [
      [
        -12.474,
        47.069
      ],
      [
        -12.474,
        47.06
      ]
    ],
    [
      [

… 87 lines total — download for the full file.

Specifications

Format: TopoJSON 1.0
Crs: WGS 84 (EPSG:4326)
Encoding: UTF-8
Line Endings: LF
Objects: 1
Polygons: 2
Arcs: 3
Shared Arcs: 1
Reversed Arc References: 1
Quantization: none
Note: arc 0 is used forward by West Field and reversed (~0) by East Field

Testing contract

Expected to pass

Scenario: Decode both polygons and test whether their shared edge is identical.
Expected result: Both rings close, both are clockwise, and the shared edge has byte-identical coordinates in each — no sliver appears between them.

What is a .topojson file?

TopoJSON is an extension of GeoJSON that encodes topology. Shared boundaries are stored once as arcs and referenced by the geometries that use them, coordinates are quantised to an integer grid and delta-encoded, and a transform object records the scale and translation needed to recover real positions. For data with many adjacent polygons — administrative boundaries especially — files are dramatically smaller than the equivalent GeoJSON.

How to use this file

Use an example .topojson file to test TopoJSON readers and GeoJSON converters, verifying that arcs are dereferenced in the right direction, that negative arc indices are handled, and that the quantisation transform is reversed exactly.

How to use this file for testing

“TopoJSON — Two Parcels Sharing One Arc” is a deterministic Novus Examples fixture for Geospatial, Conversion testing, JSON parsing. GeoJSON, GPX, and KML files with points, lines, polygons, and tracks — for testing map tools, route parsers, and geo importers.

Documented properties for this file: UTF-8 · LF · TopoJSON 1.0. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.

Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.

Geospatial fixtures publish one invented territory across formats, with the coordinate reference system and feature counts documented in specs. Convert or reproject and diff against the twin in the same group; edge-case geometries state exactly which assumption they are built to break.