Merging two polygon features (GeoJSON file) using QGIS

Question

i've seen this tutorial that explains how to merge two polygon features in QGIS.

Doing it works, but when I stop editing the layer, I got a message

Could not commit changes to layer drawingPolygons

Errors: ERROR: 1 feature(s) not added - geometry type is not compatible with the current layer.

My layer is a geoJson file. A feature looks like

{
  "type": "Feature",
  "properties": {
    "id": 632,
    "title": "",
    "media_url": "JETTE32.png",
    "media_id": 629,
    "type": "raster"
  },
  "geometry": {
    "type": "Polygon",
    "coordinates": [
      [
        [
          4.308976117998887,
          50.88773442630111
        ],
        [
          4.357000053136904,
          50.88773442630111
        ],
        [
          4.357000053136904,
          50.86630843201042
        ],
        [
          4.308976117998887,
          50.86630843201042
        ],
        [
          4.308976117998887,
          50.88773442630111
        ]
      ]
    ]
  }
}

We can see that the coordinates property is an array.

So I was thinking it would support multiple polygons, but seems it is not.

I also tested by setting "type": "MultiPolygon" instead of "type": "Polygon" by editing my geojson file with a text editor, but then it doesn't load anymore in QGIS.

Can anyone help ?

Answer 1

Multipolygon is an array of polygon coordinates. So you'll need to wrap the coordinates in another array. Try this:

{
  "type": "Feature",
  "properties": {
    "id": 632,
    "title": "",
    "media_url": "JETTE32.png",
    "media_id": 629,
    "type": "raster"
  },
  "geometry": {
    "type": "MultiPolygon",
    "coordinates": [[
      [
        [
          4.308976117998887,
          50.88773442630111
        ],
        [
          4.357000053136904,
          50.88773442630111
        ],
        [
          4.357000053136904,
          50.86630843201042
        ],
        [
          4.308976117998887,
          50.86630843201042
        ],
        [
          4.308976117998887,
          50.88773442630111
        ]
      ]
    ]]
  }
}