This heat map visualizes GDP per capita for eight countries across the years 2017–2021. It uses a sequential color scale with the `d3.interpolateTurbo` interpolator, mapping GDP values to colored cells within a banded grid. The chart is rendered as an SVG using D3 v7, with axes for location and year, a horizontal legend, and tooltips that display the exact GDP value on hover. Data is loaded from a remote CSV file via `d3.csv`.