h3-js

What is h3-js?

The h3-js npm package is a JavaScript library for working with the H3 (Hexagonal Hierarchical Geospatial Indexing System) developed by Uber. It allows for efficient spatial indexing and querying of geographic data using hexagonal grids.

What are h3-js's main functionalities?

Geo to H3

Converts a latitude and longitude to an H3 index at a specified resolution. This is useful for spatial indexing and querying.

const h3 = require('h3-js');
const lat = 37.775938728915946;
const lng = -122.41795063018799;
const resolution = 9;
const h3Index = h3.geoToH3(lat, lng, resolution);
console.log(h3Index);

H3 to Geo

Converts an H3 index back to a latitude and longitude. This is useful for decoding spatial indexes back to geographic coordinates.

const h3 = require('h3-js');
const h3Index = '8928308280fffff';
const [lat, lng] = h3.h3ToGeo(h3Index);
console.log(lat, lng);

Get Hexagon Boundary

Gets the boundary of an H3 hexagon as an array of latitude/longitude pairs. This is useful for visualizing the hexagonal grid.

const h3 = require('h3-js');
const h3Index = '8928308280fffff';
const boundary = h3.h3ToGeoBoundary(h3Index);
console.log(boundary);

K-Ring

Finds all hexagons within a given k distance from a specified H3 index. This is useful for neighborhood queries.

const h3 = require('h3-js');
const h3Index = '8928308280fffff';
const k = 1;
const kRing = h3.kRing(h3Index, k);
console.log(kRing);

Hex Ring

Finds all hexagons in a ring of a given k distance from a specified H3 index. This is useful for ring-based queries.

const h3 = require('h3-js');
const h3Index = '8928308280fffff';
const k = 1;
const hexRing = h3.hexRing(h3Index, k);
console.log(hexRing);

Other packages similar to h3-js

s2-geometry

The s2-geometry library provides tools for working with the S2 Geometry Library, which uses spherical geometry to index geographic data. Unlike H3, which uses hexagonal grids, S2 uses hierarchical cells based on the faces of a cube projected onto a sphere. This can result in different trade-offs in terms of cell shape and size consistency.

geohash

The geohash library provides tools for encoding and decoding geohashes, which are a hierarchical spatial data structure that subdivides space into buckets of grid shape. Geohashes are less uniform in cell shape compared to H3's hexagons, but they are widely used for spatial indexing and querying.

quadkey

The quadkey library provides tools for working with QuadKeys, which are a hierarchical spatial data structure used by Bing Maps. QuadKeys divide the world into a grid of squares, which can be more intuitive for certain types of spatial queries compared to H3's hexagons.

README

h3-js

The h3-js library provides a pure-JavaScript version of the H3 Core Library, a hexagon-based geographic grid system. It can be used either in Node >= 6 or in the browser. The core library is transpiled from C using emscripten, offering full parity with the C API and highly efficient operations.

For more information on H3 and for the full API documentation, please see the H3 Documentation.

• Post bug reports or feature requests to the Github Issues page
• Ask questions by posting to the H3 tag on StackOverflow

Install

npm install h3-js

Usage

:tada: Note: The following usage docs apply to H3 v4, which was released on August 23, 2022.

• For v3 docs, see the latest v3.x.x release.
• For breaking changes in v4, see the CHANGELOG. In particular, most function names have changed.

The library uses ES6 modules. Bundles for Node and the browser are built to the dist folder.

Import

ES6 usage:

import {latLngToCell} from "h3-js";

CommonJS usage:

const h3 = require("h3-js");

Pre-bundled script (library is available as an h3 global):

<script src="https://unpkg.com/h3-js"></script>

Core functions

// Convert a lat/lng point to a hexagon index at resolution 7
const h3Index = h3.latLngToCell(37.3615593, -122.0553238, 7);
// -> '87283472bffffff'

// Get the center of the hexagon
const hexCenterCoordinates = h3.cellToLatLng(h3Index);
// -> [37.35171820183272, -122.05032565263946]

// Get the vertices of the hexagon
const hexBoundary = h3.cellToBoundary(h3Index);
// -> [ [37.341099093235684, -122.04156135164334 ], ...]

Useful algorithms

// Get all neighbors within 1 step of the hexagon
const disk = h3.gridDisk(h3Index, 1);
// -> ['87283472bffffff', '87283472affffff', ...]

// Get the set of hexagons within a polygon
const polygon = [
    [37.813318999983238, -122.4089866999972145],
    [37.7198061999978478, -122.3544736999993603],
    [37.8151571999998453, -122.4798767000009008]
];
const hexagons = h3.polygonToCells(polygon, 7);
// -> ['872830828ffffff', '87283082effffff', ...]

// Get the outline of a set of hexagons, as a GeoJSON-style MultiPolygon
const coordinates = h3.cellsToMultiPolygon(hexagons, true);
// -> [[[
//      [-122.37681938644465, 37.76546768434345],
//      [-122.3856345540363,37.776004200673846],
//      ...
//    ]]]

API Reference

h3

• h3
  • .UNITS
  • .h3IndexToSplitLong(h3Index) ⇒ SplitLong
  • .splitLongToH3Index(lower, upper) ⇒ H3Index
  • .isValidCell(h3Index) ⇒ boolean
  • .isPentagon(h3Index) ⇒ boolean
  • .isResClassIII(h3Index) ⇒ boolean
  • .getBaseCellNumber(h3Index) ⇒ number
  • .getIcosahedronFaces(h3Index) ⇒ Array.<number>
  • .getResolution(h3Index) ⇒ number
  • .latLngToCell(lat, lng, res) ⇒ H3Index
  • .cellToLatLng(h3Index) ⇒ CoordPair
  • .cellToBoundary(h3Index, [formatAsGeoJson]) ⇒ Array.<CoordPair>
  • .cellToParent(h3Index, res) ⇒ H3Index
  • .cellToChildren(h3Index, res) ⇒ Array.<H3Index>
  • .cellToChildrenSize(h3Index, res) ⇒ number
  • .cellToCenterChild(h3Index, res) ⇒ H3Index
  • .cellToChildPos(h3Index, parentRes) ⇒ number
  • .childPosToCell(childPos, h3Index, childRes) ⇒ H3Index
  • .gridDisk(h3Index, ringSize) ⇒ Array.<H3Index>
  • .gridDiskDistances(h3Index, ringSize) ⇒ Array.<Array.<H3Index>>
  • .gridRingUnsafe(h3Index, ringSize) ⇒ Array.<H3Index>
  • .polygonToCells(coordinates, res, [isGeoJson]) ⇒ Array.<H3Index>
  • .cellsToMultiPolygon(h3Indexes, [formatAsGeoJson]) ⇒ Array.<Array.<Array.<CoordPair>>>
  • .compactCells(h3Set) ⇒ Array.<H3Index>
  • .uncompactCells(compactedSet, res) ⇒ Array.<H3Index>
  • .areNeighborCells(origin, destination) ⇒ boolean
  • .cellsToDirectedEdge(origin, destination) ⇒ H3Index
  • .getDirectedEdgeOrigin(edgeIndex) ⇒ H3Index
  • .getDirectedEdgeDestination(edgeIndex) ⇒ H3Index
  • .isValidDirectedEdge(edgeIndex) ⇒ boolean
  • .directedEdgeToCells(edgeIndex) ⇒ Array.<H3Index>
  • .originToDirectedEdges(h3Index) ⇒ Array.<H3Index>
  • .directedEdgeToBoundary(edgeIndex, [formatAsGeoJson]) ⇒ Array.<CoordPair>
  • .gridDistance(origin, destination) ⇒ number
  • .gridPathCells(origin, destination) ⇒ Array.<H3Index>
  • .cellToLocalIj(origin, destination) ⇒ CoordIJ
  • .localIjToCell(origin, coords) ⇒ H3Index
  • .greatCircleDistance(latLng1, latLng2, unit) ⇒ number
  • .cellArea(h3Index, unit) ⇒ number
  • .edgeLength(edge, unit) ⇒ number
  • .getHexagonAreaAvg(res, unit) ⇒ number
  • .getHexagonEdgeLengthAvg(res, unit) ⇒ number
  • .cellToVertex(h3Index, vertexNum) ⇒ H3Index
  • .cellToVertexes(h3Index) ⇒ Array.<H3Index>
  • .vertexToLatLng(h3Index) ⇒ CoordPair
  • .isValidVertex(h3Index) ⇒ boolean
  • .getNumCells(res) ⇒ number
  • .getRes0Cells() ⇒ Array.<H3Index>
  • .getPentagons(res) ⇒ Array.<H3Index>
  • .degsToRads(deg) ⇒ number
  • .radsToDegs(rad) ⇒ number
  • .H3Index : string
  • .H3IndexInput : string | Array.<number>
  • .CoordIJ
  • .H3Error
  • .CoordPair : Array.<number>
  • .SplitLong : Array.<number>

---

h3.UNITS

Length/Area units

Properties

Name	Type
m	string
m2	string
km	string
km2	string
rads	string
rads2	string

---

h3.h3IndexToSplitLong(h3Index) ⇒ SplitLong

Convert an H3 index (64-bit hexidecimal string) into a "split long" - a pair of 32-bit ints

Returns: SplitLong - A two-element array with 32 lower bits and 32 upper bits

Param	Type	Description
h3Index	H3IndexInput	H3 index to check

---

h3.splitLongToH3Index(lower, upper) ⇒ H3Index

Get a H3 index string from a split long (pair of 32-bit ints)

Returns: H3Index - H3 index

Param	Type	Description
lower	number	Lower 32 bits
upper	number	Upper 32 bits

---

h3.isValidCell(h3Index) ⇒ boolean

Whether a given string represents a valid H3 index

Returns: boolean - Whether the index is valid

Param	Type	Description
h3Index	H3IndexInput	H3 index to check

---

h3.isPentagon(h3Index) ⇒ boolean

Whether the given H3 index is a pentagon

Returns: boolean - isPentagon

Param	Type	Description
h3Index	H3IndexInput	H3 index to check

---

h3.isResClassIII(h3Index) ⇒ boolean

Whether the given H3 index is in a Class III resolution (rotated versus the icosahedron and subject to shape distortion adding extra points on icosahedron edges, making them not true hexagons).

Returns: boolean - isResClassIII

Param	Type	Description
h3Index	H3IndexInput	H3 index to check

---

h3.getBaseCellNumber(h3Index) ⇒ number

Get the number of the base cell for a given H3 index

Returns: number - Index of the base cell (0-121)

Param	Type	Description
h3Index	H3IndexInput	H3 index to get the base cell for

---

h3.getIcosahedronFaces(h3Index) ⇒ Array.<number>

Get the indices of all icosahedron faces intersected by a given H3 index

Returns: Array.<number> - Indices (0-19) of all intersected faces
Throws:

• H3Error If input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index to get faces for

---

h3.getResolution(h3Index) ⇒ number

Returns the resolution of an H3 index

Returns: number - The number (0-15) resolution, or -1 if invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index to get resolution

---

h3.latLngToCell(lat, lng, res) ⇒ H3Index

Get the hexagon containing a lat,lon point

Returns: H3Index - H3 index
Throws:

• H3Error If input is invalid

Param	Type	Description
lat	number	Latitude of point
lng	number	Longtitude of point
res	number	Resolution of hexagons to return

---

h3.cellToLatLng(h3Index) ⇒ CoordPair

Get the lat,lon center of a given hexagon

Returns: CoordPair - Point as a [lat, lng] pair
Throws:

• H3Error If input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index

---

h3.cellToBoundary(h3Index, [formatAsGeoJson]) ⇒ Array.<CoordPair>

Get the vertices of a given hexagon (or pentagon), as an array of [lat, lng] points. For pentagons and hexagons on the edge of an icosahedron face, this function may return up to 10 vertices.

Returns: Array.<CoordPair> - Array of [lat, lng] pairs
Throws:

• H3Error If input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index
[formatAsGeoJson]	boolean	Whether to provide GeoJSON output: [lng, lat], closed loops

---

h3.cellToParent(h3Index, res) ⇒ H3Index

Get the parent of the given hexagon at a particular resolution

Returns: H3Index - H3 index of parent, or null for invalid input
Throws:

• H3Error If input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index to get parent for
res	number	Resolution of hexagon to return

---

h3.cellToChildren(h3Index, res) ⇒ Array.<H3Index>

Get the children/descendents of the given hexagon at a particular resolution

Returns: Array.<H3Index> - H3 indexes of children, or empty array for invalid input
Throws:

• H3Error If resolution is invalid or output is too large for JS

Param	Type	Description
h3Index	H3IndexInput	H3 index to get children for
res	number	Resolution of hexagons to return

---

h3.cellToChildrenSize(h3Index, res) ⇒ number

Get the number of children for a cell at a given resolution

Returns: number - Number of children at res for the given cell
Throws:

• H3Error If cell or parentRes are invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index to get child count for
res	number	Child resolution

---

h3.cellToCenterChild(h3Index, res) ⇒ H3Index

Get the center child of the given hexagon at a particular resolution

Returns: H3Index - H3 index of child, or null for invalid input
Throws:

• H3Error If resolution is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index to get center child for
res	number	Resolution of cell to return

---

h3.cellToChildPos(h3Index, parentRes) ⇒ number

Get the position of the cell within an ordered list of all children of the cell's parent at the specified resolution.

Returns: number - Position of child within parent at parentRes
Throws:

• H3Error If cell or parentRes are invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index to get child pos for
parentRes	number	Resolution of reference parent

---

h3.childPosToCell(childPos, h3Index, childRes) ⇒ H3Index

Get the child cell at a given position within an ordered list of all children at the specified resolution

Returns: H3Index - H3 index of child
Throws:

• H3Error If input is invalid

Param	Type	Description
childPos	number	Position of the child cell to get
h3Index	H3IndexInput	H3 index of the parent cell
childRes	number	Resolution of child cell to return

---

h3.gridDisk(h3Index, ringSize) ⇒ Array.<H3Index>

Get all hexagons in a k-ring around a given center. The order of the hexagons is undefined.

Returns: Array.<H3Index> - H3 indexes for all hexagons in ring
Throws:

• H3Error If input is invalid or output is too large for JS

Param	Type	Description
h3Index	H3IndexInput	H3 index of center hexagon
ringSize	number	Radius of k-ring

---

h3.gridDiskDistances(h3Index, ringSize) ⇒ Array.<Array.<H3Index>>

Get all hexagons in a k-ring around a given center, in an array of arrays ordered by distance from the origin. The order of the hexagons within each ring is undefined.

Returns: Array.<Array.<H3Index>> - Array of arrays with H3 indexes for all hexagons each ring
Throws:

• H3Error If input is invalid or output is too large for JS

Param	Type	Description
h3Index	H3IndexInput	H3 index of center hexagon
ringSize	number	Radius of k-ring

---

h3.gridRingUnsafe(h3Index, ringSize) ⇒ Array.<H3Index>

Get all hexagons in a hollow hexagonal ring centered at origin with sides of a given length. Unlike kRing, this function will throw an error if there is a pentagon anywhere in the ring.

Returns: Array.<H3Index> - H3 indexes for all hexagons in ring
Throws:

• Error If the algorithm could not calculate the ring
• H3Error If input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index of center hexagon
ringSize	number	Radius of ring

---

h3.polygonToCells(coordinates, res, [isGeoJson]) ⇒ Array.<H3Index>

Get all hexagons with centers contained in a given polygon. The polygon is specified with GeoJson semantics as an array of loops. Each loop is an array of [lat, lng] pairs (or [lng, lat] if isGeoJson is specified). The first loop is the perimeter of the polygon, and subsequent loops are expected to be holes.

Returns: Array.<H3Index> - H3 indexes for all hexagons in polygon
Throws:

• H3Error If input is invalid or output is too large for JS

Param	Type	Description
coordinates	Array.<Array.<number>> | Array.<Array.<Array.<number>>>	Array of loops, or a single loop
res	number	Resolution of hexagons to return
[isGeoJson]	boolean	Whether to expect GeoJson-style [lng, lat] pairs instead of [lat, lng]

---

h3.cellsToMultiPolygon(h3Indexes, [formatAsGeoJson]) ⇒ Array.<Array.<Array.<CoordPair>>>

Get the outlines of a set of H3 hexagons, returned in GeoJSON MultiPolygon format (an array of polygons, each with an array of loops, each an array of coordinates). Coordinates are returned as [lat, lng] pairs unless GeoJSON is requested.

It is the responsibility of the caller to ensure that all hexagons in the set have the same resolution and that the set contains no duplicates. Behavior is undefined if duplicates or multiple resolutions are present, and the algorithm may produce unexpected or invalid polygons.

Returns: Array.<Array.<Array.<CoordPair>>> - MultiPolygon-style output.
Throws:

• H3Error If input is invalid

Param	Type	Description
h3Indexes	Array.<H3IndexInput>	H3 indexes to get outlines for
[formatAsGeoJson]	boolean	Whether to provide GeoJSON output: [lng, lat], closed loops

---

h3.compactCells(h3Set) ⇒ Array.<H3Index>

Compact a set of hexagons of the same resolution into a set of hexagons across multiple levels that represents the same area.

Returns: Array.<H3Index> - Compacted H3 indexes
Throws:

• H3Error If the input is invalid (e.g. duplicate hexagons)

Param	Type	Description
h3Set	Array.<H3IndexInput>	H3 indexes to compact

---

h3.uncompactCells(compactedSet, res) ⇒ Array.<H3Index>

Uncompact a compacted set of hexagons to hexagons of the same resolution

Returns: Array.<H3Index> - The uncompacted H3 indexes
Throws:

• H3Error If the input is invalid (e.g. invalid resolution)

Param	Type	Description
compactedSet	Array.<H3IndexInput>	H3 indexes to uncompact
res	number	The resolution to uncompact to

---

h3.areNeighborCells(origin, destination) ⇒ boolean

Whether two H3 indexes are neighbors (share an edge)

Returns: boolean - Whether the hexagons share an edge
Throws:

• H3Error If the input is invalid

Param	Type	Description
origin	H3IndexInput	Origin hexagon index
destination	H3IndexInput	Destination hexagon index

---

h3.cellsToDirectedEdge(origin, destination) ⇒ H3Index

Get an H3 index representing a unidirectional edge for a given origin and destination

Returns: H3Index - H3 index of the edge, or null if no edge is shared
Throws:

• H3Error If the input is invalid

Param	Type	Description
origin	H3IndexInput	Origin hexagon index
destination	H3IndexInput	Destination hexagon index

---

h3.getDirectedEdgeOrigin(edgeIndex) ⇒ H3Index

Get the origin hexagon from an H3 index representing a unidirectional edge

Returns: H3Index - H3 index of the edge origin
Throws:

• H3Error If the input is invalid

Param	Type	Description
edgeIndex	H3IndexInput	H3 index of the edge

---

h3.getDirectedEdgeDestination(edgeIndex) ⇒ H3Index

Get the destination hexagon from an H3 index representing a unidirectional edge

Returns: H3Index - H3 index of the edge destination
Throws:

• H3Error If the input is invalid

Param	Type	Description
edgeIndex	H3IndexInput	H3 index of the edge

---

h3.isValidDirectedEdge(edgeIndex) ⇒ boolean

Whether the input is a valid unidirectional edge

Returns: boolean - Whether the index is valid

Param	Type	Description
edgeIndex	H3IndexInput	H3 index of the edge

---

h3.directedEdgeToCells(edgeIndex) ⇒ Array.<H3Index>

Get the [origin, destination] pair represented by a unidirectional edge

Returns: Array.<H3Index> - [origin, destination] pair as H3 indexes
Throws:

• H3Error If the input is invalid

Param	Type	Description
edgeIndex	H3IndexInput	H3 index of the edge

---

h3.originToDirectedEdges(h3Index) ⇒ Array.<H3Index>

Get all of the unidirectional edges with the given H3 index as the origin (i.e. an edge to every neighbor)

Returns: Array.<H3Index> - List of unidirectional edges
Throws:

• H3Error If the input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index of the origin hexagon

---

h3.directedEdgeToBoundary(edgeIndex, [formatAsGeoJson]) ⇒ Array.<CoordPair>

Get the vertices of a given edge as an array of [lat, lng] points. Note that for edges that cross the edge of an icosahedron face, this may return 3 coordinates.

Returns: Array.<CoordPair> - Array of geo coordinate pairs
Throws:

• H3Error If the input is invalid

Param	Type	Description
edgeIndex	H3IndexInput	H3 index of the edge
[formatAsGeoJson]	boolean	Whether to provide GeoJSON output: [lng, lat]

---

h3.gridDistance(origin, destination) ⇒ number

Get the grid distance between two hex indexes. This function may fail to find the distance between two indexes if they are very far apart or on opposite sides of a pentagon.

Returns: number - Distance between hexagons
Throws:

• H3Error If input is invalid or the distance could not be calculated

Param	Type	Description
origin	H3IndexInput	Origin hexagon index
destination	H3IndexInput	Destination hexagon index

---

h3.gridPathCells(origin, destination) ⇒ Array.<H3Index>

Given two H3 indexes, return the line of indexes between them (inclusive).

This function may fail to find the line between two indexes, for example if they are very far apart. It may also fail when finding distances for indexes on opposite sides of a pentagon.

Notes:

• The specific output of this function should not be considered stable across library versions. The only guarantees the library provides are that the line length will be h3Distance(start, end) + 1 and that every index in the line will be a neighbor of the preceding index.
• Lines are drawn in grid space, and may not correspond exactly to either Cartesian lines or great arcs.

Returns: Array.<H3Index> - H3 indexes connecting origin and destination
Throws:

• H3Error If input is invalid or the line cannot be calculated

Param	Type	Description
origin	H3IndexInput	Origin hexagon index
destination	H3IndexInput	Destination hexagon index

---

h3.cellToLocalIj(origin, destination) ⇒ CoordIJ

Produces IJ coordinates for an H3 index anchored by an origin.

• The coordinate space used by this function may have deleted regions or warping due to pentagonal distortion.
• Coordinates are only comparable if they come from the same origin index.
• Failure may occur if the index is too far away from the origin or if the index is on the other side of a pentagon.
• This function is experimental, and its output is not guaranteed to be compatible across different versions of H3.

Returns: CoordIJ - Coordinates as an {i, j} pair
Throws:

• H3Error If the IJ coordinates cannot be calculated

Param	Type	Description
origin	H3IndexInput	Origin H3 index
destination	H3IndexInput	H3 index for which to find relative coordinates

---

h3.localIjToCell(origin, coords) ⇒ H3Index

Produces an H3 index for IJ coordinates anchored by an origin.

• The coordinate space used by this function may have deleted regions or warping due to pentagonal distortion.
• Coordinates are only comparable if they come from the same origin index.
• Failure may occur if the index is too far away from the origin or if the index is on the other side of a pentagon.
• This function is experimental, and its output is not guaranteed to be compatible across different versions of H3.

Returns: H3Index - H3 index at the relative coordinates
Throws:

• H3Error If the H3 index cannot be calculated

Param	Type	Description
origin	H3IndexInput	Origin H3 index
coords	CoordIJ	Coordinates as an {i, j} pair

---

h3.greatCircleDistance(latLng1, latLng2, unit) ⇒ number

Great circle distance between two geo points. This is not specific to H3, but is implemented in the library and provided here as a convenience.

Returns: number - Great circle distance
Throws:

• H3Error If the unit is invalid

Param	Type	Description
latLng1	Array.<number>	Origin coordinate as [lat, lng]
latLng2	Array.<number>	Destination coordinate as [lat, lng]
unit	string	Distance unit (either UNITS.m, UNITS.km, or UNITS.rads)

---

h3.cellArea(h3Index, unit) ⇒ number

Exact area of a given cell

Returns: number - Cell area
Throws:

• H3Error If the input is invalid

Param	Type	Description
h3Index	H3IndexInput	H3 index of the hexagon to measure
unit	string	Distance unit (either UNITS.m2, UNITS.km2, or UNITS.rads2)

---

h3.edgeLength(edge, unit) ⇒ number

Calculate length of a given unidirectional edge

Returns: number - Cell area
Throws:

• H3Error If the input is invalid

Param	Type	Description
edge	H3IndexInput	H3 index of the edge to measure
unit	string	Distance unit (either UNITS.m, UNITS.km, or UNITS.rads)

---

h3.getHexagonAreaAvg(res, unit) ⇒ number

Average hexagon area at a given resolution

Returns: number - Average area
Throws:

• H3Error If the input is invalid

Param	Type	Description
res	number	Hexagon resolution
unit	string	Area unit (either UNITS.m2, UNITS.km2, or UNITS.rads2)

---

h3.getHexagonEdgeLengthAvg(res, unit) ⇒ number

Average hexagon edge length at a given resolution

Returns: number - Average edge length
Throws:

• H3Error If the input is invalid

Param	Type	Description
res	number	Hexagon resolution
unit	string	Distance unit (either UNITS.m, UNITS.km, or UNITS.rads)

---

h3.cellToVertex(h3Index, vertexNum) ⇒ H3Index

Find the index for a vertex of a cell.

Returns: H3Index - Vertex index
Throws:

• H3Error If the input is invalid

Param	Type	Description
h3Index	H3IndexInput	Cell to find the vertex for
vertexNum	number	Number (index) of the vertex to calculate

---

h3.cellToVertexes(h3Index) ⇒ Array.<H3Index>

Find the indexes for all vertexes of a cell.

Returns: Array.<H3Index> - All vertex indexes of this cell
Throws:

• H3Error If the input is invalid

Param	Type	Description
h3Index	H3IndexInput	Cell to find all vertexes for

---

h3.vertexToLatLng(h3Index) ⇒ CoordPair

Get the lat, lng of a given vertex

Returns: CoordPair - Latitude, longitude coordinates of the vertex
Throws:

• H3Error If the input is invalid

Param	Type	Description
h3Index	H3IndexInput	A vertex index

---

h3.isValidVertex(h3Index) ⇒ boolean

Returns true if the input is a valid vertex index.

Returns: boolean - True if the index represents a vertex

Param	Type	Description
h3Index	H3IndexInput	An index to test for being a vertex index

---

h3.getNumCells(res) ⇒ number

The total count of hexagons in the world at a given resolution. Note that above resolution 8 the exact count cannot be represented in a JavaScript 32-bit number, so consumers should use caution when applying further operations to the output.

Returns: number - Count
Throws:

• H3Error If the resolution is invalid

Param	Type	Description
res	number	Hexagon resolution

---

h3.getRes0Cells() ⇒ Array.<H3Index>

Get all H3 indexes at resolution 0. As every index at every resolution > 0 is the descendant of a res 0 index, this can be used with h3ToChildren to iterate over H3 indexes at any resolution.

Returns: Array.<H3Index> - All H3 indexes at res 0

---

h3.getPentagons(res) ⇒ Array.<H3Index>

Get the twelve pentagon indexes at a given resolution.

Returns: Array.<H3Index> - All H3 pentagon indexes at res
Throws:

• H3Error If the resolution is invalid

Param	Type	Description
res	number	Hexagon resolution

---

h3.degsToRads(deg) ⇒ number

Convert degrees to radians

Returns: number - Value in radians

Param	Type	Description
deg	number	Value in degrees

---

h3.radsToDegs(rad) ⇒ number

Convert radians to degrees

Returns: number - Value in degrees

Param	Type	Description
rad	number	Value in radians

---

h3.H3Index : string

64-bit hexidecimal string representation of an H3 index

---

h3.H3IndexInput : string | Array.<number>

64-bit hexidecimal string representation of an H3 index, or two 32-bit integers in little endian order in an array.

---

h3.CoordIJ

Coordinates as an {i, j} pair

Properties

Name	Type
i	number
j	number

---

h3.H3Error

Custom JS Error instance with an attached error code. Error codes come from the core H3 library and can be found in the H3 docs.

Properties

Name	Type
message	string
code	number

---

h3.CoordPair : Array.<number>

Pair of lat,lng coordinates (or lng,lat if GeoJSON output is specified)

---

h3.SplitLong : Array.<number>

Pair of lower,upper 32-bit ints representing a 64-bit value

---

Legacy API

H3 v4 renamed the majority of the functions in the library. To help ease migration from H3 v3 to H3 v4, we offer a legacy API wrapper at h3-js/legacy, which exports the v4 functions with the v3 names. Users are welcome to use the legacy API wrapper as a transitional support, but are encouraged to upgrade to the H3 v4 API as soon as possible.

Note that the legacy API is not 100% backwards compatible - it's a thin wrapper on top of the v4 functions, so in cases where behavior has changed, the v4 behavior will be used. In particular, many of the v4 functions will throw errors for invalid input, where v3 functions would return null.

Installation:

npm install h3-js

Usage:

import {geoToH3} from 'h3-js/legacy';

const h3Index = geoToH3(37.3615593, -122.0553238, 7);

Development

The h3-js library uses yarn as the preferred package manager. To install the dev dependencies, just run:

yarn

To lint the code:

yarn lint

To run the tests:

yarn test

Code must be formatted with prettier; unformatted code will fail the build. To format all files:

yarn prettier

Benchmarks

The h3-js library includes a basic benchmark suite using Benchmark.js. Because many of the functions may be called over thousands of hexagons in a "hot loop", performance is an important concern. Benchmarks are run against the transpiled ES5 code by default.

To run the benchmarks in Node:

yarn benchmark-node

To run the benchmarks in a browser:

yarn benchmark-browser

Sample Node output (Macbook Pro running Node 12):

isValidCell x 3,650,995 ops/sec ±1.67% (87 runs sampled)
latLngToCell x 429,982 ops/sec ±1.39% (86 runs sampled)
cellToLatLng x 1,161,867 ops/sec ±1.11% (84 runs sampled)
cellToLatLng - integers x 1,555,791 ops/sec ±1.29% (86 runs sampled)
cellToBoundary x 375,938 ops/sec ±1.25% (87 runs sampled)
cellToBoundary - integers x 377,181 ops/sec ±1.18% (85 runs sampled)
getIcosahedronFaces x 992,946 ops/sec ±1.13% (85 runs sampled)
gridDisk x 194,400 ops/sec ±1.16% (85 runs sampled)
polygonToCells_9 x 4,919 ops/sec ±0.79% (87 runs sampled)
polygonToCells_11 x 368 ops/sec ±0.76% (86 runs sampled)
polygonToCells_10ring x 76.88 ops/sec ±0.57% (68 runs sampled)
cellsToMultiPolygon x 760 ops/sec ±1.06% (86 runs sampled)
compactCells x 2,466 ops/sec ±0.75% (86 runs sampled)
uncompactCells x 715 ops/sec ±1.15% (85 runs sampled)
areNeighborCells x 1,073,086 ops/sec ±1.56% (89 runs sampled)
cellsToDirectedEdge x 692,172 ops/sec ±1.06% (86 runs sampled)
getDirectedEdgeOrigin x 995,390 ops/sec ±1.60% (85 runs sampled)
getDirectedEdgeDestination x 930,473 ops/sec ±1.11% (86 runs sampled)
isValidDirectedEdge x 3,505,407 ops/sec ±1.05% (87 runs sampled)

When making code changes that may affect performance, please run benchmarks against master and then against your branch to identify any regressions.

Transpiling the C Source

The core library is transpiled using emscripten. The easiest way to build from source locally is by using Docker. Make sure Docker is installed, then:

yarn docker-boot
yarn build-emscripten

The build script uses the H3_VERSION file to determine the version of the core library to build. To use a different version of the library (e.g. to test local changes), clone the desired H3 repo to ./h3c and then run yarn docker-emscripten.

Contributing

Pull requests and Github issues are welcome. Please include tests for new work, and keep the library test coverage at 100%. Please note that the purpose of this module is to expose the API of the H3 Core library, so we will rarely accept new features that are not part of that API. New proposed feature work is more appropriate in the core C library or in a new JS library that depends on h3-js.

Before we can merge your changes, you must agree to the Uber Contributor License Agreement.

Versioning

The H3 core library adheres to Semantic Versioning. The h3-js library has a major.minor.patch version scheme. The major and minor version numbers of h3-js are the major and minor version of the bound core library, respectively. The patch version is incremented independently of the core library.

Legal and Licensing

The h3-js library is licensed under the Apache 2.0 License.

DGGRID Copyright (c) 2015 Southern Oregon University