GeoJSON viewer

How to use it

Drag the file onto the tool or pick it with the button: .geojson and .json both work. You’ll see every geometry on the map, a count by type, the length of the lines and the area of the polygons. In the list you can search by name or by any property value; tap a feature to highlight it on the map and see all of its properties.

Everything happens in your browser, even with large files: a 20 MB GeoJSON is read in the background without freezing the page. Nothing is uploaded to any server.

What GeoJSON is

GeoJSON is a text format, based on JSON, for storing geographic features along with their data. The current version is RFC 7946, published by the IETF in August 2016. Nearly every mapping tool reads and writes it: QGIS, Leaflet, MapLibre, Mapbox, geojson.io and libraries in every programming language.

A GeoJSON file is usually a collection of features (FeatureCollection). Each feature has a geometry and properties. Geometries can be Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon and GeometryCollection; this viewer draws all of them, including polygons with holes.

Coordinates go in longitude, latitude order, the opposite of how people usually write them. It’s the most common mistake in hand-made GeoJSON: if your points land in Antarctica or the Indian Ocean instead of where they belong, they’re probably swapped.

GeoJSON in UTM or another projection

RFC 7946 requires latitude and longitude on WGS84, but the earlier 2008 version of the format allowed other systems through a “crs” member, and plenty of software still writes it. QGIS, for example, exports in the layer’s coordinate system unless you pick EPSG:4326 when saving, which often means a UTM zone or a State Plane system.

If the file names its system, the viewer converts it to latitude and longitude and tells you: it handles UTM (WGS84, NAD83, ETRS89), Web Mercator and the national grids of the UK, Ireland, France, Spain (ED50), Portugal, Germany, Switzerland and the Netherlands. If the file doesn’t say and the coordinates are in meters, the viewer warns you and lets you pick the system. Either way, converted files come out in latitude and longitude.

Common GeoJSON problems

The JSON is broken. An extra comma at the end of a list or a missing bracket is enough to make it unreadable. If you edited it by hand, check the end of the file and the last lines you touched.

It’s too big. An unsimplified GeoJSON of boundaries can weigh hundreds of megabytes. This viewer opens up to 60 MB; for anything bigger, simplify it with mapshaper or QGIS. Too many decimals also bloat the file: 6 decimal places already give you about 10 cm of precision.

Features without geometry. GeoJSON allows features with “geometry: null” that only carry data. The viewer counts them and shows them in the list, even though they can’t appear on the map.

Converting a GeoJSON to KML, GPX or CSV

Converting to KML keeps each property’s type: numbers stay numbers and text stays text, so a code like “007” keeps its zeros. Simplestyle colors (“stroke”, “fill”, “marker-color”) become KML styles, and the “name” and “description” properties become each placemark’s name and description. You can also download a KMZ, which is smaller and opens the same way in Google Earth.

GPX has no polygons or free-form properties: polygons become closed tracks and properties go into GPX extensions. The CSV has one row per feature with its geometry as WKT, ready to import into QGIS or Google My Maps.