vega-2.json

{
  "version": 2,
  "width": 700,
  "height": 300,
  "data": [
    {
      "name": "table",
      "values": [
        {"year":1907,"population":51815},
        {"year":2011,"population":310956},
        {"year":2017,"population":269022}
      ],
      "transform": [
        {
          "type": "formula",
          "field": "date",
          "expr": "datetime(datum.year,1,1)"
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "time",
      "range": "width",
      "domain": {
        "data": "table",
        "field": "date"
      }
    },
    {
      "name": "y",
      "type": "linear",
      "range": "height",
      "domain": {
        "data": "table",
        "field": "population"
      }
    }
  ],
  "marks": [
    {
      "type": "line",
      "from": {"data": "table"},
      "properties": {
        "enter": {
          "x": {"scale": "x","field": "date"},
          "y": {"scale": "y","field": "population"},
          "stroke": {"value": "#99B2CC"},
          "strokeWidth": {"value": 3},
          "interpolate": {"value": "monotone"}
        }
      }
    }
  ]
}