Table Heatmap

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "data": {"url": "data/cars.json"},
  "mark": "rect",
  "encoding": {
    "y": {"field": "Origin", "type": "nominal"},
    "x": {"field": "Cylinders", "type": "ordinal"},
    "color": {"aggregate": "mean", "field": "Horsepower", "type": "quantitative"}
  }
}