A bubble chart displays the correlation between the area in square kilometers, GDP in billion USD, and population in millions for major U.S. cities. The visualization uses D3.js v7, rendering SVG circles whose x-position maps population, y-position maps area, and radius encodes GDP. A color scale, derived from the city names via `d3.interpolateTurbo` and `d3.scaleOrdinal`, distinguishes each city, while a tooltip shows the city on hover. The code also includes a legend for bubble size and interactive hover effects.