GeoJSON — the universal format

GeoJSON (RFC 7946) is the de facto interchange format for geographic data. It's what every mapping library reads and writes, and it has several sharp edges that trip up developers.

Geometry types

GeoJSON has nine types:

Feature and FeatureCollection are the wrapper types you'll use most. Raw geometry types (Point, Polygon, etc.) carry no attributes; wrapping them in a Feature lets you attach a properties object with metadata like names, IDs, and display values.

{
  ype] "Feature",
  "geometry": {
    ype] "Point",
    "coordinates": [
      74.3587,
      31.5204
    ]
  },
  "properties": {
    "name": "Lahore",
    "population": 13000000
  }
}

The lon/lat trap

GeoJSON coordinates are [longitude, latitude] — the opposite of most mapping APIs.

{ "type": "Point", "coordinates": [74.3587, 31.5204] }
//                                  ^ lon first   ^ lat second

Google Maps, Apple Maps, Leaflet — they all use (lat, lon). GeoJSON follows the (x, y) = (easting, northing) convention from cartography. This trips up every developer at least once.

// ❌ Wrong — swapped
const point = { type: "Point", coordinates: [31.5204, 74.3587] };

// ✅ Correct
const point = { type: "Point", coordinates: [74.3587, 31.5204] };

Winding order (right-hand rule)

RFC 7946 requires counter-clockwise exterior rings and clockwise interior rings (holes). This is the right-hand rule: if you walk the boundary with your right hand pointing outward, the interior is to your left.

Counter-clockwise exterior (correct):       Clockwise interior/hole (correct):
  [0,1] → [1,1] → [1,0] → [0,0] → [0,1]     [0.2,0.8] → [0.2,0.2] → [0.8,0.2] → [0.8,0.8]

Winding order matters because GeoJSON needs a convention to distinguish the "inside" from the "outside" of a polygon, especially for global-spanning polygons where either side could be the interior. Some consumers (Mapbox, PostGIS) auto-correct winding order. Others reject invalid GeoJSON silently. Always validate.

import { rewind } from "@turf/rewind";
const corrected = rewind(myGeoJSON, { reverse: false });