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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.
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:
consth3=require("h3-js");
Pre-bundled script (library is available as an h3 global):
<scriptsrc="https://unpkg.com/h3-js"></script>
Core functions
// Convert a lat/lng point to a hexagon index at resolution 7consth3Index=h3.latLngToCell(37.3615593,-122.0553238,7);// -> '87283472bffffff'// Get the center of the hexagonconsthexCenterCoordinates=h3.cellToLatLng(h3Index);// -> [37.35171820183272, -122.05032565263946]// Get the vertices of the hexagonconsthexBoundary=h3.cellToBoundary(h3Index);// -> [ [37.341099093235684, -122.04156135164334 ], ...]
Useful algorithms
// Get all neighbors within 1 step of the hexagonconstdisk=h3.gridDisk(h3Index,1);// -> ['87283472bffffff', '87283472affffff', ...]// Get the set of hexagons within a polygonconstpolygon=[[37.813318999983238,-122.4089866999972145],[37.7198061999978478,-122.3544736999993603],[37.8151571999998453,-122.4798767000009008]];consthexagons=h3.polygonToCells(polygon,7);// -> ['872830828ffffff', '87283082effffff', ...]// Get the outline of a set of hexagons, as a GeoJSON-style MultiPolygonconstcoordinates=h3.cellsToMultiPolygon(hexagons,true);// -> [[[// [-122.37681938644465, 37.76546768434345],// [-122.3856345540363,37.776004200673846],// ...// ]]]
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 cell index
Returns: boolean - Whether the cell index is valid
Param
Type
Description
h3Index
H3IndexInput
H3 index to check
h3.isValidIndex(h3Index) ⇒ boolean
Whether a given string represents a valid H3 index
(e.g. it may be a cell, directed edge, vertex.)
Use isValidCell to check for a valid
hexagon (or pentagon) cell ID.
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.getIndexDigit(h3Index, digit) ⇒ number
Get the number of the indexing digit for an H3 index
Returns: number - Digit (0-7)
Param
Type
Description
h3Index
H3IndexInput
H3 index to get the digit for
digit
number
Indexing digit to get the valeu of
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
Creates a cell from its components (resolution, base cell number, and indexing digits).
This is the inverse operation of getResolution, getBaseCellNumber, and getIndexDigit.
Only allows creating valid cells.
Returns: H3Index - H3 index Throws:
H3Error If input is invalid
Param
Type
Description
baseCellNumber
number
Base cell number of cell to return
digits
Array.<number>
Indexing digits of cell to return
res
number
Resolution of cell to return. Optional, if not specified, will be inferred from digits.
h3.latLngToCell(lat, lng, res) ⇒ H3Index
Get the hexagon (or pentagon) 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 cell to return
h3.cellToLatLng(h3Index) ⇒ CoordPair
Get the lat,lon center of a given hexagon (or pentagon)
Returns: CoordPair - Point as a [lat, lng] pair Throws:
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:
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 to allocate
Param
Type
Description
h3Index
H3IndexInput
H3 index of center hexagon
ringSize
number
Radius of k-ring
h3.gridRing(h3Index, ringSize) ⇒ Array.<H3Index>
Get all hexagons in a hollow hexagonal ring centered at origin with sides of a given length.
Returns: Array.<H3Index> - H3 indexes for all hexagons in ring Throws:
Error If the algorithm could not calculate the ring
Get all hexagons in a hollow hexagonal ring centered at origin with sides of a given length.
Unlike gridDisk, 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
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
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
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.
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.reverseDirectedEdge(edgeIndex) ⇒ H3Index
Returns the directed edge with origin and destination cells reversed
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
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.
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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.
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.
