This visualization demonstrates five distinct marks and channels—x-position, y-position, length, size, and shape—each rendered on separate SVG layers using d3-selection. The x-position layer maps population income groups to horizontal coordinates and life expectancy estimates to vertical positions, colored via d3.schemeCategory10. The hue channel uses d3.schemeCategory10 to color circles, while length encodes values through rectangle heights, size through circle radii, and shape through d3.symbol with predefined symbol types. The React-based interface includes a Dropdown component for user interaction.