sample1.vl

{
    "hconcat": [
        {
            "mark": "point",
            "encoding": {
                "x": {
                    "field": "Horsepower",
                    "type": "quantitative"
                },
                "y": {
                    "field": "Miles_per_Gallon",
                    "type": "quantitative"
                }
            }
        },
        {
            "transform": [
                {
                    "sample": 200
                }
            ],
            "mark": "point",
            "encoding": {
                "x": {
                    "field": "Horsepower",
                    "type": "quantitative"
                },
                "y": {
                    "field": "Miles_per_Gallon",
                    "type": "quantitative"
                }
            }
        }
    ],
    "data": {
        "url": "https://vega.github.io/vega-lite/data/cars.json"
    },
    "$schema": "https://vega.github.io/schema/vega-lite/v3.json"
}