This example displays a bar chart of the world’s most populous countries, using the population data from `data.csv`. The visualization renders a single large rectangle for each country, with the rectangle’s width and height fixed at 300 pixels. The code loads the CSV with `d3.csv`, converts the population values to numbers, and appends SVG `rect` elements using `select('svg')` and `selectAll('rect').data(data).enter().append`.