Introduction to GeoJSON files

A GeoJSON file is used to store geometry and associated properties.

A minimal example would be:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "id": "a",
      "properties": {
        "name": "Point A"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [0, 0]
      }
    }
  ]
}

GeoJSON is widely supported across many platforms and applications. It doesn’t require specialist tools to view, and there is nothing proprietary about the format. Specifically, GeoJSON is a JavaScript Object Notation (JSON) file with standardised properties and structure.

Because GeoJSON files are just text, you can view their content in most text editors

The GeoJSON RFC7946 standard

Because GeoJSON has been around for a while, there are a number of non-standard additions that other applications have added over the years. While the bulk of the file may look similar to others, there could be things such as top-level properties that entirely change the coordinate system of the features, or the winding order of the polygons.

To try and align everyone’s files, an RFC was produced that defines the dos and don’ts for GeoJSON: RFC7946. This document is extremely verbose and goes into a level of detail that the average user will never need. Most applications allow the user to request an output file that follows the spec.

GeoJSON files that do not follow RFC7946 may not display correctly in Cadence

Other geometry file types

When we talk about file-based geometry, GeoJSON is one of dozens of formats available to choose from. When gathering files from the internet, you’ll likely come across other examples such as GeoPackages, Shapefiles and GML.

Cadence only supports GeoJSON. Other file types will need to be converted to GeoJSON (RFC7946) for use in Cadence.