This visualization shows the five most populous countries each year, using a bar chart that sorts countries by population descending and displays the population values for each. The data is loaded from a CSV file containing population by country and year, which is fetched using the `d3.csv` function. The visualization is built using the `vega-lite-api` library, with the chart specification defined in `viz.js` using the `vl.markBar()` and `vl.encode()` methods. The rendering is handled by `vega` and `vega-lite`, with interactive tooltips enabled through `vega-tooltip`.