dotMap1.vl

{
    "transform": [
        {
            "as": "digit",
            "calculate": "substring(datum.zip_code, 0, 1)"
        }
    ],
    "height": 300,
    "mark": "circle",
    "data": {
        "url": "https://vega.github.io/vega-lite/data/zipcodes.csv"
    },
    "width": 500,
    "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
    "projection": {
        "type": "albersUsa"
    },
    "encoding": {
        "color": {
            "field": "digit",
            "type": "nominal"
        },
        "size": {
            "value": 1
        },
        "latitude": {
            "field": "latitude",
            "type": "quantitative"
        },
        "longitude": {
            "field": "longitude",
            "type": "quantitative"
        }
    },
    "description": "US zip codes: One dot per zipcode colored by first digit"
}