# proj4js/proj4js

JavaScript library to transform coordinates from one coordinate system to another, including datum transformations

Repository: https://github.com/proj4js/proj4js
Canonical: https://ross.abutalabs.com/products/proj4js
Homepage: http://proj4js.github.io/proj4js/
Language: JavaScript
License: NOASSERTION
License Family: other
Topics: epsg, gis, geospatial, javascript, datum-transformations
Last push: 2026-08-12T11:01:46+00:00

## Health v2 (maintenance only)
Score: 97/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 97, release rhythm 95, longevity 100
- inputs: {"age_days": 4828, "days_push": 21, "days_rel": 37, "gap_med": 3, "n_releases_24m": 30}
- flags: no_license
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2239, forks 352 (observed 2026-08-28T04:06:29.663784+00:00)

## What it is
Proj4js is a JavaScript library for transforming point coordinates between coordinate reference systems, including datum transformations. It is a port of PROJ.4 and GCTCP C, accepting proj strings, WKT, and PROJJSON projection definitions.

## Use cases
- convert lat/lon coordinates to a projected CRS like UTM or state plane
- reproject GeoJSON coordinates between EPSG codes in the browser
- transform coordinates from WGS84 to a custom proj string projection
- perform datum transformations between NAD83 and WGS84
- parse WKT or PROJJSON projection definitions in JavaScript
- reproject map tile coordinates for a web mapping app

## When to choose
- you need coordinate/datum transformations in JavaScript for Node or the browser
- you work with EPSG codes, proj strings, WKT, or PROJJSON definitions
- you need a lightweight, dependency-free reprojection library for web mapping

## When to avoid
- you need the full PROJ feature set, grids, or newest datum models — use native PROJ instead
- you are not working in JavaScript
- you need raster or image reprojection rather than point coordinates

## Facets
- artifact type: library
- maturity: stable
- function: geospatial, parser, math
- domain: web-development
- platform: browser, cross-platform
- tags: coordinate-transformation, projection, epsg, datum-transformation, gis, wkt, proj, geospatial, maps, javascript, nodejs

## Member repositories
- proj4js/proj4js (main) score 97

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:29.663784+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:44:10.418292+00:00, confidence not recorded.
  - readme: https://github.com/proj4js/proj4js (fetched 2026-08-28T04:06:29.663784+00:00, sha 96c60f6c5e5e)
  - homepage: http://proj4js.github.io/proj4js/ (fetched 2026-08-29T10:24:43.751693+00:00, sha 79b15acf2ab6)
  - registry_npm: https://registry.npmjs.org/proj4js (fetched 2026-08-29T10:24:43.754383+00:00, sha 33fe87b80cd5)
- Data as of 2026-08-30T08:39:29.467469+00:00.