This bar chart displays the relationship between BMI and age group from a heart disease dataset. Each bar represents the BMI value for a specific age category, plotted along the x-axis. The chart uses D3.js v4 with SVG rendering, specifically leveraging `d3.scaleBand` for the categorical x-axis and `d3.scaleLinear` for the continuous y-axis. The data is loaded from a CSV file using `d3.csv`, and bars are drawn as SVG rectangles with the class "bar". Axes are added using `d3.axisBottom` and `d3.axisLeft`.