Spatial Data Format of the Week: GeoJSON

The Web-Native Vector Format

File extension: .geojson or .json

What it is: A lightweight, human-readable format for encoding geographic data structures using JavaScript Object Notation (JSON). It's the modern standard for web mapping and API data exchange.

The Single-File Simplicity

Unlike shapefiles (which require 3-15 files), GeoJSON is one self-contained file:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates": [-122.375, 37.619]
      },
      "properties": {
        "name": "San Francisco International Airport",
        "iata_code": "SFO",
        "passengers_annual": 57800000
      }
    }
  ]
}

Why Web Developers Love It

Advantages

1. Web-Friendly by Design

Native JavaScript format—no parsing libraries needed
Direct integration with web mapping libraries (Leaflet, Mapbox, D3)
Perfect for APIs and web services
Readable by humans and machines

2. No Artificial Limitations

Field names can be any length: population_density_2020_census_tract_estimate
Unlimited fields per feature
No 2GB component file limits
Single file—no missing companions

3. Flexible Data Structures

Supports nested attributes: {"address": {"street": "123 Main", "city": "Palo Alto"}}
Arrays: "languages": ["English", "Spanish", "Mandarin"]
Boolean values: "is_active": true
Null values: "elevation": null
Mixed data types within properties

4. Modern Ecosystem

GitHub renders GeoJSON automatically
Observable, Jupyter, and Colab support native display
Extensive JavaScript library support
Direct browser viewing without GIS software

The Performance Trade-offs

Limitations

1. No Spatial Indexing

Every spatial query requires scanning the entire file
Slow for large datasets (>50,000 features)
Desktop GIS software may struggle with rendering

2. File Size Bloat

Text format is larger than binary formats
Coordinate precision stored as full decimal strings
Redundant structure for repeated property names

3. Coordinate System Ambiguity

Assumed WGS 84 (EPSG:4326) unless specified
No embedded .prj file—CRS must be in metadata
Reprojection requires explicit handling

4. Not Optimized for Analysis

Designed for display and transport, not complex spatial operations
QGIS/ArcGIS prefer shapefiles for heavy analysis
Better suited for web visualization than desktop workflows

When to Use GeoJSON

Best for:

Web mapping applications
API responses and data exchange
GitHub/GitLab spatial data (auto-renders)
Interactive web visualizations (D3, Leaflet, Mapbox)
Simple geometries with rich attributes
Data under ~50MB / ~50,000 features

Avoid when:

Large datasets requiring spatial indexes
Desktop GIS analysis workflows
File sizes exceed 50MB
Performance is critical (use tiles or GeoPackage)

Creating GeoJSON in QGIS

Right-click layer → Export → Save Features As
Format: GeoJSON
File name: my_data.geojson
CRS: EPSG:4326 - WGS 84 (recommended for web)
Encoding: UTF-8
Coordinate precision: 6-8 decimal places (balance precision vs. file size)
Click OK

GeoJSON vs. Shapefile: The Decision Matrix

Criterion	GeoJSON	Shapefile
Use case	Web mapping, APIs	Desktop GIS, analysis
File structure	Single file	3-15 files
Field name length	Unlimited	10 characters max
File size limit	~50MB practical	2GB per component
Spatial indexing	No	Yes (.sbn/.sbx)
Web compatibility	Native JavaScript	Requires conversion
Human readable	Yes	No (binary)
Desktop GIS performance	Slow on large files	Fast with indexes

Advanced: GeoJSON Variants

GeoJSONL (GeoJSON Lines)

One feature per line (newline-delimited)
Streamable for large datasets
Used by Tippecanoe, Mapbox, and big data pipelines

{"type":"Feature","geometry":{"type":"Point","coordinates":[-122.375,37.619]},"properties":{"name":"SFO"}}
{"type":"Feature","geometry":{"type":"Point","coordinates":[-0.454,51.470]},"properties":{"name":"LHR"}}

TopoJSON

Optimized encoding eliminating redundant coordinates
Shared borders (topology preservation)
~80% smaller file sizes
Used for choropleth maps with shared boundaries

Web Mapping with GeoJSON

Leaflet example:

fetch('airports.geojson')
  .then(response => response.json())
  .then(data => {
    L.geoJSON(data, {
      onEachFeature: (feature, layer) => {
        layer.bindPopup(feature.properties.name);
      }
    }).addTo(map);
  });

D3.js example:

d3.json('counties.geojson').then(data => {
  svg.selectAll('path')
    .data(data.features)
    .enter().append('path')
    .attr('d', d3.geoPath());
});

The Bottom Line

GeoJSON is the format for modern web mapping. If your data will appear in a web browser, display in a JavaScript application, or pass through an API, choose GeoJSON. If you're doing heavy spatial analysis in desktop GIS, stick with shapefiles or GeoPackage.

Key takeaway: Shapefiles for analysis, GeoJSON for the web.

SDFotW - GeoJSON Format