A choropleth map of Michigan ZIP code tabulation areas visualizes population density using an azimuthal equal-area projection, with each postal region colored by its population-per-land-area ratio. The visualization uses D3.js's `geoAzimuthalEqualArea` projection and `geoPath` to render SVG paths, overlaying administrative boundaries from TopoJSON. Population data from Michigan-demographics.com is joined with ZIP code geometries, and a linear scale maps density values to opacity levels between 0.3 and 1. Hovering reveals the ZIP code and total population.