val milanoGridDF = spark.read
    .schema(geojsonSchema)
    .json("data/Milano/milano-grid/milano-grid.geojson")
    .select(explode(col("features")).as("lala"))
    .select(col("lala").as[Features])
    .map(f => (f.properties.cellId, f.geometry.coordinates))
    .toDF("square_id", "coordinates")