Becker's Barley Trellis Plot

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "name": "trellis_barley",
  "description": "The Trellis display by Becker et al. helped establish small multiples as a “powerful mechanism for understanding interactions in studies of how a response depends on explanatory variables”. Here we reproduce a trellis of Barley yields from the 1930s, complete with main-effects ordering to facilitate comparison.",
  "data": {"url": "data/barley.json"},
  "mark": "point",
  "encoding": {
    "row": {
      "field": "site", "type": "ordinal",
      "sort": {"op": "median", "field": "yield"}
    },
    "x": {
      "aggregate": "median", "field": "yield", "type": "quantitative",
      "scale": {"zero": false}
    },
    "y": {
      "field": "variety", "type": "ordinal",
      "sort": {"field": "yield","op": "median", "order": "descending"},
      "scale": {"rangeStep": 12}
    },
    "color": {"field": "year", "type": "nominal"}
  }
}