{
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:EPSG::3857" } },
"features": [
{ "type": "Feature", "properties": { "id_a": "A1" }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 3.0, 3.0 ], [ 3.0, 7.0 ], [ 6.0, 7.0 ], [ 6.0, 3.0 ], [ 3.0, 3.0 ] ] ] } }
]
}