map1d.vl

{
    "height": 400,
    "width": 500,
    "$schema": "https://vega.github.io/schema/vega-lite/v3.json",
    "layer": [
        {
            "mark": {
                "stroke": "white",
                "fill": "lightgrey",
                "type": "geoshape"
            },
            "data": {
                "url": "https://gicentre.github.io/data/geoTutorials/londonBoroughs.json",
                "format": {
                    "feature": "boroughs",
                    "type": "topojson"
                }
            }
        },
        {
            "mark": "circle",
            "data": {
                "url": "https://gicentre.github.io/data/geoTutorials/londonCentroids.csv"
            },
            "encoding": {
                "latitude": {
                    "field": "cy",
                    "type": "quantitative"
                },
                "longitude": {
                    "field": "cx",
                    "type": "quantitative"
                }
            }
        },
        {
            "mark": "circle",
            "data": {
                "url": "https://gicentre.github.io/data/geoTutorials/londonCentroids.csv"
            },
            "encoding": {
                "latitude": {
                    "value": 51.28
                },
                "longitude": {
                    "field": "cx",
                    "type": "quantitative"
                }
            }
        },
        {
            "mark": "circle",
            "data": {
                "url": "https://gicentre.github.io/data/geoTutorials/londonCentroids.csv"
            },
            "encoding": {
                "latitude": {
                    "field": "cy",
                    "type": "quantitative"
                },
                "longitude": {
                    "value": -0.52
                }
            }
        }
    ]
}