This visualization displays the number of participant countries in each Winter Olympics from 1924 to 2018, with each circle representing a year. The code computes participant counts by aggregating unique country names per year using a JavaScript `Set` within a `reduce` operation. It uses D3.js scales and axes to map years and counts, and renders circles with a fixed radius and reduced opacity to show the trend. Data comes from a Kaggle dataset of Winter Olympic medals.