{ "$schema": "https://vega.github.io/schema/vega-lite/v4.json", "data": {"url": "data/cars.json"}, "mark": "circle", "encoding": { "x": {"field": "Horsepower", "type": "quantitative"}, "y": {"field": "Miles_per_Gallon", "type": "quantitative"}, "opacity": {"field": "Miles_per_Gallon", "type": "quantitative"} }}