Rectangular Brush

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "Drag out a rectangular brush to highlight points.",
  "data": {"url": "data/cars.json"},
  "params": [{
    "name": "brush",
    "select": "interval",
    "value": {"x": [55, 160], "y": [13, 37]}
  }],
  "mark": "point",
  "encoding": {
    "x": {"field": "Horsepower", "type": "quantitative"},
    "y": {"field": "Miles_per_Gallon", "type": "quantitative"},
    "color": {
      "condition": {"param": "brush", "field": "Cylinders", "type": "ordinal"},
      "value": "grey"
    }
  }
}