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Guide

How to download GeoJSON or KML from a web map

The short answer: if the map is backed by a WFS, a FeatureServer, or OGC API Features, ask it for GeoJSON directly. If it is backed by a static file, save the file. If it is tiles, you cannot, and you should go looking for the source instead.

Check for the easy one first

Before anything clever: open the network tab (F12, Network, reload) and look for a single request pulling a .geojson, .json, .kml, .kmz, or .zip.

A lot of web maps are one static file and some JavaScript. If you see one, that is the entire dataset in a single request. Right-click it, Open in new tab, and save the page. You are finished.

This is the case people skip past on their way to something more complicated.

Asking a service for GeoJSON

From a WFS

https://example.com/wfs?SERVICE=WFS&VERSION=2.0.0&REQUEST=GetFeature
  &TYPENAMES=council:parcels&OUTPUTFORMAT=application/json&COUNT=1000

TYPENAMES is the layer's <Name> from the capabilities document, not the friendly title. What GetCapabilities tells you covers finding it, and also whether the service will give you JSON at all: check the outputFormat list first. Some only offer GML, which QGIS reads fine.

From an Esri FeatureServer

https://services.arcgis.com/AbC/arcgis/rest/services/Parcels/FeatureServer/0/query
  ?where=1=1&outFields=*&f=geojson

Swap f=geojson for f=json if you want Esri JSON. Getting data out of an ArcGIS web map has the full parameter list.

From OGC API Features

https://example.com/collections/parcels/items?limit=1000&f=json

The newest and the tidiest of the three: it speaks GeoJSON natively.

Getting only the bit you want

This is the part worth learning, because "download everything then clip it" is how you end up waiting twenty minutes for a national dataset to answer a question about one suburb, while somebody else's server carries the cost.

By bounding box. Every service takes one:

  • WFS: &BBOX=166.4,-47.3,178.6,-34.4,EPSG:4326
  • Esri: &geometry=166.4,-47.3,178.6,-34.4&geometryType=esriGeometryEnvelope&inSR=4326
  • OGC API: &bbox=166.4,-47.3,178.6,-34.4

By attribute. Esri takes real SQL in where:

&where=SUBURB='Thorndon' AND AREA_HA > 2

WFS takes a CQL filter, if the server supports it:

&CQL_FILTER=suburb='Thorndon'

Count first. On Esri, &returnCountOnly=true tells you what you are about to ask for before you ask for it. Worth doing every time.

Paging, when there is a lot

Servers cap what they return: typically 1000 or 2000 features. Ask for 40,000 and you silently get 1000, which is the failure mode that ruins an analysis quietly rather than loudly.

Esri:

&resultRecordCount=1000&resultOffset=0
&resultRecordCount=1000&resultOffset=1000

WFS:

&COUNT=1000&STARTINDEX=0
&COUNT=1000&STARTINDEX=1000

Increment until you get a short page back. Always check the count against what you expected. A round number like exactly 1000 is a truncation, not a coincidence.

Getting KML or a shapefile

GeoJSON is what services speak. For anything else, convert:

  • QGIS: add the layer, right-click, Export, Save Features As, and pick KML, shapefile, GeoPackage, or whatever you need.
  • ogr2ogr, if you would rather: ogr2ogr -f KML out.kml in.geojson.

Some WFS servers will do it for you: check the capabilities for SHAPE-ZIP in the outputFormat list, and if it is there you can have a shapefile built on demand.

Doing it without the URL surgery

Handling bounding boxes, paging, and format parameters by hand is fine once and tedious after that.

Geo Hound has a download dialog on any service that supports it: pick a layer, draw a bounding box on a small map rather than working out coordinates, add attribute filters with a builder, and it tells you the feature count before you commit. You get GeoJSON out.

For WMS, which serves pictures rather than features, the same dialog exports an image for your drawn area instead, at a size and format you choose.

And once a layer is in the workbench, every layer card has a download menu: GeoJSON, KML, CSV, Excel, or a zipped shapefile, straight out of the browser.

When the answer is no

If the map is drawing raster tiles, there is no data to download. Each tile is a picture. See how to find the XYZ tile URL for what that does and does not get you, and extracting GIS data from a website for what to do instead.

Whatever you do get: check the licence on the portal before you republish it.