Scatterplot with External Links and Tooltips

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "description": "A scatterplot showing horsepower and miles per gallons that opens a Google search for the car that you click on.",
  "data": {"url": "data/cars.json"},
  "mark": "point",
  "transform": [{
    "calculate": "'https://www.google.com/search?q=' + datum.Name", "as": "url"
  }],
  "encoding": {
    "x": {"field": "Horsepower", "type": "quantitative"},
    "y": {"field": "Miles_per_Gallon", "type": "quantitative"},
    "color": {"field": "Origin", "type": "nominal"},
    "tooltip": {"field": "Name", "type": "nominal"},
    "href": {"field": "url", "type": "nominal"}
  }
}