A choropleth map of Oklahoma counties displays student-to-teacher ratios, with an interactive range slider. The map’s fill colors update over time as users drag the slider from 1987 to 2010. The visualization is built with D3 v7, using `d3.geoConicConformal`, `d3.geoPath`, and `topojson.feature` to render map shapes from a loaded JSON file. The slider event triggers a `switch` to update county colors based on yearly data.