This example shows hourly Air Quality Index (AQI) readings across multiple Chinese cities, with each city’s time series plotted as an area chart and stacked vertically for comparison. The visualization uses a Vega-Lite specification embedded via `vegaEmbed`, which declares temporal x-axes, quantitative y-axes, and row facets for city names. Data is loaded from a CSV file using `d3.csv`, and the chart re-renders on window resize by re-calling `vegaEmbed` with updated dimensions. The code references D3 v4 for data loading and Vega-Lite v2 for the visual encoding.