TopoJSON — Zero-Length Arc
A topology whose fourth arc repeats the same position twice, giving a line of zero length. Quantization produces these routinely when two vertices land in the same grid cell, and simplification code that divides by segment length fails on them.
{
"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
]
]
},
{
"type": "LineString",
"id": "Z-001",
"properties": {
"name": "Zero-length survey leg",
"defect": "arc has no extent"
},
"arcs": [
3
]
}
]
}
},
"arcs": [
[Specifications
- Format
- TopoJSON 1.0
- Crs
- WGS 84 (EPSG:4326)
- Encoding
- UTF-8
- Line Endings
- LF
- Objects
- 1
- Arcs
- 4
- Degenerate Arcs
- 1
- Arc Length Degrees
- 0
- Quantization
- none
- Note
- arc 3 repeats a single position
Testing contract
Expected to pass- Scenario
- Decode the topology and simplify or measure the resulting geometries.
- Expected result
- The zero-length line decodes without a division-by-zero; it is either dropped with a note or kept as a degenerate LineString, never turned into NaN coordinates.
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 — Zero-Length Arc” 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 · 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.
Related files
- geojsonGeoJSON — Antimeridian Line Split per RFC 7946The same transect cut at the 180th meridian into a two-part MultiLineString, which is what RFC 7946 section 3.1.9 recommends. The split latitude is the linear interpolation of the unsplit twin, so the two files describe the same ground path.
- geojsonGeoJSON — Antimeridian Polygon Split into a MultiPolygonThe straddling block cut at 180 into two polygons that share an edge on the meridian — the interoperable form. Use it as the expected output when testing an antimeridian-splitting routine against the unsplit twin.
- geojsonGeoJSON — Clockwise Exterior Ring (right-hand rule violated)Both rings of the Mill Court parcel are wound the wrong way round: the exterior clockwise, the interior counter-clockwise. RFC 7946 mandates the right-hand rule, and consumers that rely on winding to tell holes from shells will read this polygon inside out.
- geojsonGeoJSON — Intentionally Invalid: Hole Outside Its ShellIntentionally invalid: the second ring is a whole separate parcel filed as an interior ring of the first, which OGC Simple Features forbids. It is what happens when a MultiPolygon is flattened into a Polygon by concatenating rings.
- geojsonGeoJSON — Intentionally Invalid: Latitude Before LongitudeIntentionally invalid: the five towns with their coordinates written latitude-first. RFC 7946 fixes the order as longitude then latitude, and this is the mistake that arrives via an EPSG-URN-ordered source such as the GML twin in the territory subcategory.
- geojsonGeoJSON — Intentionally Invalid: Self-Intersecting RingIntentionally invalid: a bowtie ring whose two lobes wind in opposite directions, so the shoelace areas nearly cancel. Buffer, intersection and area operations on this geometry return nonsense rather than failing, which is why it belongs in a validation suite.
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