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What is GeoJSON? A Planner's Introduction

By · Last updated April 26, 2026 · 8 min read

If you've tried to download parcel data or work with mapping tools, you've run into GeoJSON files. This guide covers what GeoJSON is, why it matters for planning work, and how to use it without becoming a GIS expert.

GeoJSON in Plain English

GeoJSON is a file format for storing geographic data (points, lines, and polygons) along with information about each feature.

Think of it as a spreadsheet for maps:

  • Shapefile = the old way (multiple files, proprietary)
  • GeoJSON = the modern way (single file, open standard, web-friendly)

What Does GeoJSON Look Like?

A simplified example of a single parcel in GeoJSON format:

{
  "type": "Feature",
  "properties": {
    "APN": "001-234-56",
    "OWNER": "SMITH, JOHN",
    "MAIL_ADDR": "123 Main St",
    "MAIL_CITY": "Anytown",
    "MAIL_STATE": "CA",
    "MAIL_ZIP": "90001"
  },
  "geometry": {
    "type": "Polygon",
    "coordinates": [[[-118.2, 34.0], [-118.2, 34.1], ...]]
  }
}
Key insight: A GeoJSON file is plain text. Open it in any text editor to see what's inside. No special software required.

The Three Parts of a GeoJSON Feature

Part What It Contains Example for Parcels
type Always "Feature" for individual items "Feature"
properties Attribute data (the "spreadsheet" part) Owner name, APN, mailing address
geometry The shape and location Polygon coordinates defining parcel boundary

Geometry Types You'll Encounter

Point

A single location. Used for addresses, project sites, or any feature shown as a dot on a map.

"geometry": {
  "type": "Point",
  "coordinates": [-118.2437, 34.0522]
}

Polygon

A closed shape. Used for parcels, zoning districts, neighborhoods, or any area.

"geometry": {
  "type": "Polygon",
  "coordinates": [[[-118.25, 34.05], [-118.24, 34.05], ...]]
}

LineString

A line made of connected points. Used for streets, boundaries, or routes.

MultiPolygon

Several separate polygons treated as one feature. Common for parcels with detached portions or islands.

For planning work: You'll mostly work with Polygons (parcels, zones) and Points (addresses, project sites). Skip the other types until you need them.

FeatureCollection: The Container

In practice you rarely work with a single Feature. You'll have a FeatureCollection: a container that holds many features.

{
  "type": "FeatureCollection",
  "features": [
    { /* parcel 1 */ },
    { /* parcel 2 */ },
    { /* parcel 3 */ },
    // ... hundreds or thousands more
  ]
}

A county's parcel file can contain 100,000+ features in a single FeatureCollection.

Coordinates: How Location Works

GeoJSON uses longitude, latitude order, the opposite of what Google Maps shows. Both are in decimal degrees:

  • Longitude = East-West position (negative values = West of Prime Meridian)
  • Latitude = North-South position (positive values = Northern Hemisphere)
Common gotcha: GeoJSON uses [longitude, latitude], but most maps display as "latitude, longitude." If your parcels appear near Africa when you expected California, check the coordinate order.

Properties: The Data You Care About

For public notice work, the properties object holds the useful data. County parcel files often include:

Common Field What It Contains
APN / PARCEL_ID Assessor's Parcel Number
OWNER / OWNER_NAME Property owner name
MAIL_ADDR Mailing address street
MAIL_CITY Mailing address city
MAIL_STATE Mailing address state
MAIL_ZIP Mailing address ZIP code
SITUS_ADDR Property street address
Important: Field names vary by county. One county might use OWNER_NAME while another uses OWNERNAME or OWN_NAME. UrbanKit Studio lets you map your fields when uploading data.

Where to Get GeoJSON Parcel Data

See our detailed guide: How to Get Parcel GeoJSON Data from Your County GIS

Quick sources:

  • County GIS portals — Search "[County Name] GIS open data"
  • State clearinghouses — Some states aggregate parcel data statewide
  • Commercial providers — Regrid, LightBox, CoreLogic

Working with Large Files

County-wide parcel files can be huge (50-200MB). To handle them:

  • Don't open in a text editor — Use a tool like mapshaper.org
  • Clip to your area — Extract the parcels you need before uploading
  • Simplify geometry — Cuts file size with little visual impact

Common Issues and Fixes

File Too Large

County-wide parcel files can be 100MB+. Solutions:

  • Use mapshaper to clip to your project area before uploading
  • Simplify geometry (reduces detail but shrinks file size)
  • Request a subset from your county GIS department

Wrong Coordinate System

If your parcels appear in the wrong location (off the coast of Africa, for example), they're in a local projection instead of WGS84. Use QGIS or mapshaper to reproject to EPSG:4326.

Missing or Garbled Properties

Attribute data sometimes doesn't transfer cleanly, especially with special characters. Check the original data source and re-export if needed.

"Invalid GeoJSON" Errors

Common causes:

  • File is actually a different format (shapefile component, KML, etc.)
  • File is corrupted or truncated (incomplete download)
  • JSON syntax error (missing bracket or comma)

Validate at geojsonlint.com for specific error messages.

Ready to use your GeoJSON parcel data?

Open the Radius Notice Generator →

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