Clicking a wedge of this donut chart rotates the entire pie so that the selected segment lands at the bottom, while the age-group labels counter-rotate to remain upright. Built with D3 v4, it uses `d3.pie` and `d3.arc` for geometry, SVG paths for rendering, and a transition on the group’s `transform` attribute over one second. The color scale maps seven population age brackets, and the label rotation is reversed via `label.centroid` calculations.