This example displays a map of Slovakia with circles positioned at the centroids of each district, sized according to the number of apartments in multi-story residential buildings. The map uses a Mercator projection via `d3.geoMercator` and `d3.geoPath`, with topojson data loaded asynchronously. Circle sizes are scaled using `d3.scaleLinear`, and a legend is generated with a custom `sizeLegend` function. The visualization is rendered as SVG in a React app and supports zooming through D3’s zoom behavior.