This bar chart shows the number of scientists by country, using a dataset that lists each scientist's field and major discovery. The chart is built with D3 v7 and rendered as an SVG. It uses `d3.rollups` to count occurrences per country, then `scaleBand` and `scaleLinear` to map the data to bar positions and heights. The visualization includes labeled axes, a title, and a legend, and is centered on a light blue background with a custom margin and styling.