GeoJSON stands for Geographic JSON—it's a format for encoding geographic data structures using JSON (JavaScript Object Notation).

In short, it's a way to represent points, lines, shapes, and features on a map using a structure that's easy to read, share, and use in code.

Key Parts of GeoJSON

A GeoJSON object usually includes:

1. type – Describes the kind of data ("Feature", "Point", "Polygon", etc.)
2. geometry – The actual geographic shape (location, area, path)
3. properties – Extra info about the place or shape (name, population, type of site, etc.)

Example: A Point Feature

json
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{
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [-73.9857, 40.7484]
  },
  "properties": {
    "name": "Empire State Building",
    "city": "New York"
  }
}

• type: "Feature" means this is a single mappable thing.
• geometry:
  • "Point" is the type of shape.
  • coordinates are [longitude, latitude].
• properties: Custom details you can attach—anything you want.

Types of Geometry

GeoJSON supports several geometry types:

• "Point" – A single location
• "LineString" – A path (like a road)
• "Polygon" – An area (like a park or country)
• "MultiPoint" / "MultiPolygon" / "MultiLineString" – Groups of those
• "GeometryCollection" – A mix of multiple geometry types

Object Literals versus GeoJSON Features

An object literal is just a basic JSON object—a set of key-value pairs used to represent any kind of data.

A GeoJSON Feature is a structured object used specifically to represent geographic data. It follows a standard format, so that mapping tools can understand and render it properly.

Projected versus Unprojected Geometries

When working with geographic data on maps, it’s important to understand the difference between unprojected and projected geometries. GeoJSON stores coordinates in an unprojected format—specifically, latitude and longitude values based on the WGS84 coordinate system. However, for accurate measurements, transformations, and on-screen rendering, those coordinates often need to be projected into a flat, Cartesian coordinate system. This section explains how and why that projection happens, and how it affects geometry manipulation in real-world mapping tools.

Unprojected Geometries (aka Geographic Coordinates)

GeoJSON typically uses geographic coordinates:

• Longitude (x) and Latitude (y)
• Like: [ -73.9857, 40.7484 ] (NYC-ish)

json
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{
  "type": "Point",
  "coordinates": [-73.9857, 40.7484]
}

But these are not Cartesian—they're on a curved Earth (spherical or ellipsoidal)

• This format assumes the Earth is a globe (WGS84 is the default system in GeoJSON).
• These coordinates are not evenly spaced in terms of distance:
  • 1° of longitude is not the same distance everywhere on Earth.
  • Shapes look distorted near the poles.

Projected Geometries (aka Cartesian Coordinates)

• These coordinates have been flattened from the curved Earth to a 2D surface (like a map or screen).
• They are typically in meters or pixels.
• They allow for precise measurements and transformations.

Examples of projections:

• Globe → most accurate (Giraffe 3D basemaps)
• Web Mercator → most common, think the map on your elementary school wall (EPSG:3857) (Giraffe 2D basemaps)
• UTM → local, meter-based projections for accurate surveying.
• Albers Equal Area, Lambert Conformal Conic → great for preserving area or shape at larger scales.

<aside> 👉

Learn more about setting your project’s projection in Set the project CRS

</aside>

This would be the same location as before, but now in projected meters (e.g., Web Mercator).

json
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{
  "type": "Point",
  "coordinates": [1335832.46, 6261723.78]
}

Cartesian Coordinates

• When you project geographic coordinates, they become Cartesian:
  • X = east-west
  • Y = north-south
• These are used in math to:
  • Measure distances (Euclidean)
  • Rotate/move/scale shapes
  • Align layers correctly on maps

So when we say "Cartesian" in mapping, we’re usually talking about projected coordinates—flattened into an (x, y) system.

So Why Use Projected or Unprojected?

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