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This example shows a choropleth map of the United States, with states colored by whether the author has lived in, visited, or never visited them. Overlaid circles mark cities where the author has resided, with circle size scaled by years spent there. Hovering a circle reveals a tooltip with the city name. The visualization is built with D3 v3, using `d3.geo.albersUsa` and `d3.geo.path` to render GeoJSON state boundaries, while a linear color scale and SVG circles encode the categorical and quantitative data.