example.geojson

{
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": {
                "name": "Custom Shape"
            },
            "geometry": {
                "type": "Polygon",
                "coordinates": [
                    [
                        [-20, 0],
                        [-20, 20],
                        [0, 20],
                        [0, 0],
                        [-20, 0]
                    ]
                ]
            }
        }
    ]
}