topojson1.2 KB

TopoJSON — Intentionally Invalid: Arc Referenced Without Reversal

Intentionally invalid: East Field references the shared arc forwards when it should use the reversed form, so its ring no longer closes. This is the single most common hand-editing mistake in TopoJSON, and it produces a plausible-looking file that renders as a torn shape.

Geospatial Error handling Conversion testing

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": [
            [
              0,
              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
Defect: intentionally invalid — East Field references arc 0 forward instead of ~0
Ring Closes: false
Valid: false

Testing contract

Expected to fail

Scenario: Decode the topology and check that every polygon ring closes.
Expected result: West Field closes; East Field does not, because the arc it reuses runs in the wrong direction — a decoder should report the open ring rather than auto-closing it.

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 — Intentionally Invalid: Arc Referenced Without Reversal” is a deterministic Novus Examples fixture for Geospatial, Error handling, Conversion testing. 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 · intentionally invalid. 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.