This example visualizes United States GDP data from FreeCodeCamp, rendering a bar chart in SVG where each bar represents quarterly GDP values. The chart uses D3.js v4 with a linear y-scale and an x-axis showing years, fetched from a remote JSON source. The code employs `d3.scaleLinear`, `d3.axisLeft`, and `d3.axisBottom` to map data to bar heights and positions, with bars styled via CSS classes.