This stacked bar chart visualizes the estimated 2010 religious breakdown of the 20 most populous countries, using data from the Pew Research Center. Each bar shows a country’s total population segmented by religion, with tooltips revealing exact values on hover. The visualization uses D3 v3’s `d3.layout.stack`, `d3.scale.ordinal`, and `d3.svg.axis`. The color legend is built with `d3.legend`, and highlighting a religion in the legend dims other bars via a semi-transparent overlay while redrawing the selected layer in a foreground group. The SVG rendering includes a custom SI tick formatter that converts billions to “B.”