function addSizeLegend() {
    legend_size
        .visible(true)
        .update();

    let max_radius = max(data.data, d=> parseFloat(getSizeValue(d.value)))

	const scale = scaleSqrt()
		.domain([0, max_radius])
		.range([0, max_radius]);

    legend_size
        .scale(scale)
        .update();
}