This pie chart visualizes the age distribution of a population, with each slice labeled by age group and its percentage shown in a text tooltip on mouseover. The chart is built with D3.js v3, using `d3.layout.pie` for the pie layout and `d3.svg.arc` for the arc paths and hover geometry. The visualization reads data from a CSV file containing age categories and population counts, and the slices expand slightly on hover to highlight the selected segment.