A choropleth map of Slovakia encodes the number of apartments in apartment buildings per district as circles, scaled by a linear `d3.scaleLinear` and positioned at each district’s centroid via `d3.geoCentroid` and a `geoMercator` projection. Districts render as SVG paths from TopoJSON data, with hover highlighting, while a separate `sizeLegend` provides tick labels. The map supports zooming and panning through `d3.zoom` and uses `d3.tsv` and `d3.json` to load and join tabular census data.