topojson6.6 KB

TopoJSON — Three Named Objects in One Topology

One topology carrying three separately named objects — towns, roads and areas — that all index into the same arc pool. This is how a single TopoJSON file ships what would otherwise be three layers, and readers that assume exactly one object silently show only the first.

Geospatial Conversion testing JSON parsing

Preview — first 50 linestopojson

{
  "type": "Topology",
  "objects": {
    "towns": {
      "type": "GeometryCollection",
      "geometries": [
        {
          "type": "Point",
          "properties": {
            "name": "Kestrel Bay",
            "code": "KB",
            "kind": "town",
            "population": 4820,
            "founded": 1786
          },
          "coordinates": [
            -12.482,
            47.064
          ]
        },
        {
          "type": "Point",
          "properties": {
            "name": "Marram",
            "code": "MR",
            "kind": "town",
            "population": 1180,
            "founded": 1834
          },
          "coordinates": [
            -12.3915,
            47.112
          ]
        },
        {
          "type": "Point",
          "properties": {
            "name": "Holloway",
            "code": "HW",
            "kind": "town",
            "population": 2670,
            "founded": 1801
          },
          "coordinates": [
            -12.551,
            47.018
          ]
        },
        {
          "type": "Point",

… 416 lines total — download for the full file.

Specifications

Format: TopoJSON 1.0
Crs: WGS 84 (EPSG:4326)
Encoding: UTF-8
Line Endings: LF
Objects: 3
Object Names: towns, roads, areas
Arcs: 10
Quantization: none
Shared Arc Pool: true

Testing contract

Expected to pass

Scenario: Load the file and enumerate the objects before converting any of them.
Expected result: Three objects are listed by name and each converts independently; no object is skipped and the arc pool is shared rather than duplicated.

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 — Three Named Objects in One Topology” 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.