validate

All validation functions return a result object with the following shape:

{
  valid: boolean,        // whether the object is valid
  errors: { message: string, path?: string, index?: number }[],
  warnings: { message: string, path?: string, index?: number }[]
}

Errors indicate structural or semantic invalidity. Warnings are non-blocking observations (e.g. high coordinate precision, antimeridian crossing, missing geometry).

Paths use a JSON Pointer-like notation: /coordinates/0, /features/2/geometry, /bbox.

Errors and warnings reference

Errors

Emitted by	Message pattern	Cause
`validatePosition`	`Invalid coordinates: longitude must be in the range -180 to 180`	Longitude out of range
`validatePosition`	`Invalid coordinates: latitude must be in the range -90 to 90`	Latitude out of range
`validatePosition`	`Invalid coordinates: altitude must be a number`	Altitude is not a finite number
`validateBBox`	`Invalid bbox: must be an array of 4 or 6 numbers`	Wrong length or wrong type
`validateBBox`	`Invalid bbox: south-west corner — …`	SW corner fails position validation
`validateBBox`	`Invalid bbox: north-east corner — …`	NE corner fails position validation
`validateBBox`	`Invalid bbox: south (N) must be <= north (M)`	South latitude exceeds north
`validateCRS`	`Invalid crs: unknown type: …`	`type` is neither `name` nor `link`
`validateCRS`	`Invalid crs: named crs must have a non-empty properties.name string`	Missing or empty `properties.name`
`validateCRS`	`Invalid crs: linked crs must have a non-empty properties.href string`	Missing or empty `properties.href`
`validateGeometry`	`Invalid geometry type: …`	Unknown `type` value
`validateGeometry`	`Invalid LinearRing: first and last position must be identical`	Ring is not closed
`validateGeometry`	`Invalid LinearRing: must have at least 4 positions`	Ring has fewer than 4 positions
`validateGeometry`	`Invalid LinearRing: self-intersection detected`	Ring crosses itself
`validateGeoJson`	`Invalid GeoJson: type must be either a Geometry, a Feature or a FeatureCollection`	Unknown root type
`validateGeoJson`	`Invalid FeatureCollection: features must be a non empty array`	`features` is empty or not an array

Warnings

Emitted by	Message pattern	Cause
`validatePosition`	`longitude precision is high (N decimals, max recommended: 6)`	Longitude has more than 6 decimal digits
`validatePosition`	`latitude precision is high (N decimals, max recommended: 6)`	Latitude has more than 6 decimal digits
`validateBBox`	`bbox crosses the antimeridian (west: N > east: M)`	West > east in a bounding box
`validateGeometry`	`LineString crosses the antimeridian between positions N and M, consider using MultiLineString`	Segment jumps across the antimeridian
`validateGeometry`	`Polygon outer ring should be counter-clockwise`	Outer ring has clockwise winding
`validateGeometry`	`Polygon hole ring should be clockwise`	A hole ring has counter-clockwise winding
`validateGeoJson`	`Feature has no geometry`	`geometry` is `null` or absent

Behavioral notes

Winding order

The GeoJSON specification (RFC 7946 §3.1.6) mandates that polygon rings follow a specific winding order: the outer ring must be counter-clockwise and holes must be clockwise (both when viewed on a standard map with north up). Violations emit a warning, not an error, to stay compatible with data produced by tools that do not enforce winding order.

// Outer ring is clockwise → warning
validateGeometry({
  type: 'Polygon',
  coordinates: [[[0, 0], [0, 1], [1, 1], [1, 0], [0, 0]]]
})
// { valid: true, errors: [], warnings: [{ message: 'Polygon outer ring should be counter-clockwise' }] }

// Outer ring CCW, hole CCW → warning on the hole
validateGeometry({
  type: 'Polygon',
  coordinates: [
    [[0, 0], [0, 10], [10, 10], [10, 0], [0, 0]],  // outer CCW ✓
    [[2, 2], [2, 8], [8, 8], [8, 2], [2, 2]]        // hole should be CW ✗
  ]
})
// { valid: true, errors: [], warnings: [{ message: 'Polygon hole ring should be clockwise' }] }

Antimeridian crossings

A segment is considered to cross the antimeridian when the absolute difference between the longitudes of two consecutive positions exceeds 180°. When this happens, validateGeometry emits a warning and suggests splitting the geometry into a MultiLineString or MultiPolygon. validateBBox emits a warning when west > east.

validateGeometry({ type: 'LineString', coordinates: [[170, 0], [-170, 0]] })
// { valid: true, errors: [], warnings: [{ message: 'LineString crosses the antimeridian between positions 0 and 1, consider using MultiLineString' }] }

validateBBox([170, -20, -170, 20])
// { valid: true, errors: [], warnings: [{ message: 'bbox crosses the antimeridian (west: 170 > east: -170)' }] }

Self-intersections

Self-intersections are checked on Polygon and MultiPolygon rings. A ring self-intersects when any two non-adjacent edges cross. This produces an error.

validateGeometry({
  type: 'Polygon',
  coordinates: [[[0, 0], [2, 2], [0, 2], [2, 0], [0, 0]]] // bowtie shape
})
// { valid: false, errors: [{ message: 'Invalid LinearRing: self-intersection detected' }], warnings: [] }

Coordinate precision

More than 6 decimal digits on longitude or latitude (~0.1 mm resolution) produces a warning. The value is still considered valid.

validatePosition([2.35221234, 48.8566])
// { valid: true, errors: [], warnings: [{ message: 'longitude precision is high (8 decimals, max recommended: 6)' }] }

CRS support

The crs property was removed from the GeoJSON specification in RFC 7946 but remains present in older data and in some GIS exports. validateGeoJson validates the crs object if present at the root of a Feature or FeatureCollection. Two types are supported: name and link.

validateGeoJson({
  type: 'FeatureCollection',
  features: [{ type: 'Feature', geometry: { type: 'Point', coordinates: [0, 0] }, properties: {} }],
  crs: { type: 'name', properties: { name: 'urn:ogc:def:crs:OGC:1.3:CRS84' } }
})
// { valid: true, errors: [], warnings: [] }

validatePosition

Signature

validatePosition (coordinates)

Description

Validates a GeoJSON position. Checks that it is an array of 2 or 3 finite numbers, that longitude is in [-180, 180] and latitude in [-90, 90]. Emits a warning if longitude or latitude precision exceeds 6 decimal digits.

Non-finite values (NaN, Infinity, -Infinity) and non-number elements (null, strings) are rejected.

Parameters

Name	Type	Required	Description
`coordinates`	`number[]`	yes	A position array `[longitude, latitude]` or `[longitude, latitude, altitude]`

Returns

Type	Description
`object`	Validation result

Examples

validatePosition([2.3522, 48.8566])
// { valid: true, errors: [], warnings: [] }

validatePosition([2.3522, 48.8566, 35])
// { valid: true, errors: [], warnings: [] }

validatePosition([200, 48.8566])
// { valid: false, errors: [{ message: 'Invalid coordinates: longitude must be in the range -180 to 180' }], warnings: [] }

validatePosition([0, -91])
// { valid: false, errors: [{ message: 'Invalid coordinates: latitude must be in the range -90 to 90' }], warnings: [] }

validatePosition([NaN, 48])
// { valid: false, errors: [{ message: 'Invalid coordinates: longitude must be in the range -180 to 180' }], warnings: [] }

validatePosition([2.35221234, 48.8566])
// { valid: true, errors: [], warnings: [{ message: 'longitude precision is high (8 decimals, max recommended: 6)' }] }

validateBBox

Signature

validateBBox (bbox)

Description

Validates a GeoJSON bounding box. Accepts 4-value (2D) and 6-value (3D) arrays. Validates both the south-west and north-east corners as positions. Checks that south ≤ north. Emits a warning if west > east (antimeridian crossing). Precision warnings from corner positions are forwarded.

Parameters

Name	Type	Required	Description
`bbox`	`number[]`	yes	A bounding box: `[west, south, east, north]` or `[west, south, minAlt, east, north, maxAlt]`

Returns

Type	Description
`object`	Validation result

Examples

validateBBox([-10, -20, 10, 20])
// { valid: true, errors: [], warnings: [] }

validateBBox([-10, -10, 0, 10, 10, 100])
// valid 3D bbox: { valid: true, errors: [], warnings: [] }

validateBBox([-10, 30, 10, 20])
// { valid: false, errors: [{ message: 'Invalid bbox: south (30) must be <= north (20)' }], warnings: [] }

validateBBox([170, -20, -170, 20])
// { valid: true, errors: [], warnings: [{ message: 'bbox crosses the antimeridian (west: 170 > east: -170)' }] }

validateCRS

Signature

validateCRS (crs)

Description

Validates a GeoJSON CRS (Coordinate Reference System) object. Supports two types: name (requires a non-empty properties.name string) and link (requires a non-empty properties.href string). The optional type field on a link CRS is not validated.

Parameters

Name	Type	Required	Description
`crs`	`object`	yes	A CRS object

Returns

Type	Description
`object`	Validation result

Examples

validateCRS({ type: 'name', properties: { name: 'urn:ogc:def:crs:OGC:1.3:CRS84' } })
// { valid: true, errors: [], warnings: [] }

validateCRS({ type: 'link', properties: { href: 'https://example.com/crs', type: 'proj4' } })
// { valid: true, errors: [], warnings: [] }

validateCRS({ type: 'link', properties: { href: '' } })
// { valid: false, errors: [{ message: 'Invalid crs: linked crs must have a non-empty properties.href string' }], warnings: [] }

validateCRS({ type: 'unknown' })
// { valid: false, errors: [{ message: 'Invalid crs: unknown type: unknown' }], warnings: [] }

validateGeometry

Signature

validateGeometry (geometry, path = '')

Description

Validates a GeoJSON geometry object. Dispatches validation based on geometry.type. Validates coordinates recursively for all geometry types. For Polygon and MultiPolygon, checks that rings are closed (first and last position identical), have at least 4 positions, follow the correct winding order, and contain no self-intersections. For LineString and MultiLineString, warns on antimeridian crossings. If a bbox is present, it is validated as well.

The path parameter is used internally when called from validateGeoJson to produce accurate error paths (e.g. /features/2/geometry). You do not need to pass it directly.

Parameters

Name	Type	Required	Description
`geometry`	`object`	yes	A GeoJSON geometry object
`path`	`string`	no	Base path for error and warning reporting (default: `''`)

Returns

Type	Description
`object`	Validation result

Examples

validateGeometry({ type: 'Point', coordinates: [2.3522, 48.8566] })
// { valid: true, errors: [], warnings: [] }

validateGeometry({ type: 'LineString', coordinates: [[0, 0], [1, 1]] })
// { valid: true, errors: [], warnings: [] }

// Unclosed ring
validateGeometry({ type: 'Polygon', coordinates: [[[0, 0], [1, 0], [1, 1], [0, 0]]] })
// { valid: false, errors: [{ message: 'Invalid LinearRing: first and last position must be identical', path: '/coordinates/0' }], warnings: [] }

// Antimeridian crossing
validateGeometry({ type: 'LineString', coordinates: [[170, 0], [-170, 0]] })
// { valid: true, errors: [], warnings: [{ message: 'LineString crosses the antimeridian between positions 0 and 1, consider using MultiLineString', path: '/coordinates' }] }

// Self-intersecting polygon (bowtie)
validateGeometry({ type: 'Polygon', coordinates: [[[0, 0], [2, 2], [0, 2], [2, 0], [0, 0]]] })
// { valid: false, errors: [{ message: 'Invalid LinearRing: self-intersection detected', path: '/coordinates/0' }], warnings: [] }

validateGeometry({ type: 'Unknown', coordinates: [] })
// { valid: false, errors: [{ message: 'Invalid geometry type: Unknown' }], warnings: [] }

validateGeoJson

Signature

validateGeoJson (geoJson)

Description

Validates any GeoJSON object: a geometry, a Feature, or a FeatureCollection. Dispatches to validateGeometry for plain geometries. For Feature, validates the geometry if present, and emits a warning if geometry is null or absent. For FeatureCollection, validates each feature recursively and reports the index of any invalid feature. If a crs property is present at the root, it is validated as well.

Parameters

Name	Type	Required	Description
`geoJson`	`object`	yes	Any GeoJSON object

Returns

Type	Description
`object`	Validation result

Throws

Throws a TypeError if geoJson is not a non-empty plain object.

Examples

validateGeoJson({ type: 'Point', coordinates: [2.3522, 48.8566] })
// { valid: true, errors: [], warnings: [] }

validateGeoJson({
  type: 'Feature',
  geometry: { type: 'Point', coordinates: [2.3522, 48.8566] },
  properties: {}
})
// { valid: true, errors: [], warnings: [] }

// Feature with no geometry
validateGeoJson({ type: 'Feature', geometry: null, properties: {} })
// { valid: true, errors: [], warnings: [{ message: 'Feature has no geometry' }] }

// Invalid coordinate inside a FeatureCollection — error includes path and index
validateGeoJson({
  type: 'FeatureCollection',
  features: [
    { type: 'Feature', geometry: { type: 'Point', coordinates: [0, 0] }, properties: {} },
    { type: 'Feature', geometry: { type: 'Point', coordinates: [200, 48.8566] }, properties: {} }
  ]
})
// {
//   valid: false,
//   errors: [{
//     message: 'Invalid coordinates: longitude must be in the range -180 to 180',
//     path: '/features/1/geometry/coordinates',
//     index: 1
//   }],
//   warnings: []
// }

// Empty features array
validateGeoJson({ type: 'FeatureCollection', features: [] })
// { valid: false, errors: [{ message: 'Invalid FeatureCollection: features must be a non empty array' }], warnings: [] }

// CRS validated when present
validateGeoJson({
  type: 'FeatureCollection',
  features: [{ type: 'Feature', geometry: { type: 'Point', coordinates: [0, 0] }, properties: {} }],
  crs: { type: 'link', properties: { href: '' } }
})
// { valid: false, errors: [{ message: 'Invalid crs: linked crs must have a non-empty properties.href string' }], warnings: [] }

validate ​

Errors and warnings reference ​

Errors ​

Warnings ​

Behavioral notes ​

Winding order ​

Antimeridian crossings ​

Self-intersections ​

Coordinate precision ​

CRS support ​

validatePosition ​

Signature ​

Description ​

Parameters ​

Returns ​

Examples ​

validateBBox ​

Signature ​

Description ​

Parameters ​

Returns ​

Examples ​

validateCRS ​

Signature ​

Description ​

Parameters ​

Returns ​

Examples ​

validateGeometry ​

Signature ​

Description ​

Parameters ​

Returns ​

Examples ​

validateGeoJson ​

Signature ​

Description ​

Parameters ​

Returns ​

Throws ​

Examples ​

validate

Errors and warnings reference

Errors

Warnings

Behavioral notes

Winding order

Antimeridian crossings

Self-intersections

Coordinate precision

CRS support

validatePosition

Signature

Description

Parameters

Returns

Examples

validateBBox

Signature

Description

Parameters

Returns

Examples

validateCRS

Signature

Description

Parameters

Returns

Examples

validateGeometry

Signature

Description

Parameters

Returns

Examples

validateGeoJson

Signature

Description

Parameters

Returns

Throws

Examples