This visualization presents a multi-line chart tracking life expectancy against GDP across several countries over a 15-year period. The chart uses color to represent different years in five-year increments, while line thickness encodes the average BMI for each data series. The code loads a WHO life expectancy CSV dataset, parses the year column, and nests the data by GDP value using `d3.nest()`. It renders the chart through the Metrics Graphics library (MG), with `MG.data_graphic()` managing the axes, legend, and series styling, while D3 v4 handles custom number formatting for the y-axis.