Tukey Box Plot (1.5 IQR)

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "description": "A vertical 2D box plot showing median, min, and max in the US population distribution of age groups in 2000.",
  "data": {
    "url": "data/population.json"
  },
  "transform": [
    {
      "aggregate": [
        {
          "op": "q1",
          "field": "people",
          "as": "lowerBox"
        },
        {
          "op": "q3",
          "field": "people",
          "as": "upperBox"
        },
        {
          "op": "median",
          "field": "people",
          "as": "midBox"
        }
      ],
      "groupby": [
        "age"
      ]
    },
    {
      "calculate": "datum.upperBox - datum.lowerBox",
      "as": "IQR"
    },
    {
      "calculate": "datum.lowerBox - datum.IQR * 1.5",
      "as": "lowerWhisker"
    },
    {
      "calculate": "datum.upperBox + datum.IQR * 1.5",
      "as": "upperWhisker"
    }
  ],
  "layer": [
    {
      "mark": {
        "type": "rule",
        "style": "boxWhisker"
      },
      "encoding": {
        "y": {
          "field": "lowerWhisker",
          "type": "quantitative",
          "axis": {
            "title": "population"
          }
        },
        "y2": {
          "field": "lowerBox",
          "type": "quantitative"
        },
        "x": {
          "field": "age",
          "type": "ordinal"
        }
      }
    },
    {
      "mark": {
        "type": "rule",
        "style": "boxWhisker"
      },
      "encoding": {
        "y": {
          "field": "upperBox",
          "type": "quantitative"
        },
        "y2": {
          "field": "upperWhisker",
          "type": "quantitative"
        },
        "x": {
          "field": "age",
          "type": "ordinal"
        }
      }
    },
    {
      "mark": {
        "type": "bar",
        "style": "box"
      },
      "encoding": {
        "y": {
          "field": "lowerBox",
          "type": "quantitative"
        },
        "y2": {
          "field": "upperBox",
          "type": "quantitative"
        },
        "x": {
          "field": "age",
          "type": "ordinal"
        },
        "size": {
          "value": 5
        }
      }
    },
    {
      "mark": {
        "type": "tick",
        "style": "boxMid"
      },
      "encoding": {
        "y": {
          "field": "midBox",
          "type": "quantitative"
        },
        "x": {
          "field": "age",
          "type": "ordinal"
        },
        "color": {
          "value": "white"
        },
        "size": {
          "value": 5
        }
      }
    }
  ]
}