This fork of a D3 v7 area chart example displays two linked visualizations: a green line chart and a red area chart, both plotting age against monthly income. The code loads CSV data from a GitHub gist, filters invalid entries, and sorts by age before rendering smooth monotone curves on separate SVG elements. Interactive tooltips appear on mouseover of the line chart’s circles, showing the precise age and income values. Both charts share identical linear scales, axes, and margins, with the area chart using the same monotone curve for its filled region.