{
  "$schema": "https://vega.github.io/schema/vega-lite/v3.json",
  "data": {"url": "data/cars.json"},
  "encoding": {
    "x": {
      "field": "Year",
      "type": "temporal",
      "timeUnit": "year", "band": 0.5
    }
  },
  "layer": [
    {
      "mark": {"type": "errorband", "extent": "ci"},
      "encoding": {
        "y": {
          "field": "Miles_per_Gallon",
          "type": "quantitative",
          "title": "Mean of Miles per Gallon (95% CIs)"
        }
      }
    },
    {
      "mark": "line",
      "encoding": {
        "y": {
          "aggregate": "mean",
          "field": "Miles_per_Gallon",
          "type": "quantitative"
        }
      }
    }
  ]
}