This line chart displays population estimates for four animal groups—birds, cats, dogs, and fish—across multiple countries, using a multi-line layout to compare trends by country. The visualization renders as an SVG and uses D3 v5 APIs including `d3.csv`, `scaleLinear`, `scaleOrdinal`, `axisBottom`, `axisLeft`, and `nest` to structure the data. Color encodes animal type via `schemeCategory10`, while the axes show country and population values. The chart is built from `data.csv` and styled with external CSS.