
            // initialize the chart; 
            renderinit(data);

            const area = d3.area()
            .curve(d3.curveCardinal.tension(0.3)) // default is d3.curveLinear, d3.curveBundle.beta(1.0)
            .x(d => xScale(xValue(d.data)))
            .y0(d => yScale(d[0]))
            .y1(d => yScale(d[1]));

            const area_hubei = d3.area()
            .curve(d3.curveCardinal.tension(0.3))
            .x((d) => xScale(xValue(d.data)))
            .y0(d => nyScale(d[0]))
            .