{
    "data": {
        "url": "https://vega.github.io/vega-lite/data/seattle-weather.csv"
    },
    "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
    "layer": [
        {
            "mark": "bar",
            "encoding": {
                "x": {
                    "field": "date",
                    "timeUnit": "month",
                    "type": "ordinal"
                },
                "y": {
                    "field": "precipitation",
                    "aggregate": "mean",
                    "type": "quantitative"
                }
            }
        },
        {
            "mark": "rule",
            "encoding": {
                "color": {
                    "value": "red"
                },
                "size": {
                    "value": 3
                },
                "y": {
                    "field": "precipitation",
                    "aggregate": "mean",
                    "type": "quantitative"
                }
            }
        }
    ],
    "description": "Monthly precipitation with mean value overlay"
}