Line Chart Example

Line charts are used to depict changing values, with line slopes conveying rates of change. Different interpolators change the curvature of the line. Options such as cardinal or Catmull-Rom interpolation can produce pleasing curves, but can also “hallucinate” maximum or minimum values that do not exist in the data. Use monotone interpolation for smooth curves that faithfully preserve monotonicity.

Vega JSON Specification <>

{
  "$schema": "https://vega.github.io/schema/vega/v3.0.json",
  "width": 500,
  "height": 200,
  "padding": 5,

  "signals": [
    {
      "name": "interpolate",
      "value": "linear",
      "bind": {
        "input": "select",
        "options": [
          "basis",
          "cardinal",
          "catmull-rom",
          "linear",
          "monotone",
          "natural",
          "step",
          "step-after",
          "step-before"
        ]
      }
    }
  ],

  "data": [
    {
      "name": "table",
      "values": [
        {"x": 0, "y": 28, "c":0}, {"x": 0, "y": 20, "c":1},
        {"x": 1, "y": 43, "c":0}, {"x": 1, "y": 35, "c":1},
        {"x": 2, "y": 81, "c":0}, {"x": 2, "y": 10, "c":1},
        {"x": 3, "y": 19, "c":0}, {"x": 3, "y": 15, "c":1},
        {"x": 4, "y": 52, "c":0}, {"x": 4, "y": 48, "c":1},
        {"x": 5, "y": 24, "c":0}, {"x": 5, "y": 28, "c":1},
        {"x": 6, "y": 87, "c":0}, {"x": 6, "y": 66, "c":1},
        {"x": 7, "y": 17, "c":0}, {"x": 7, "y": 27, "c":1},
        {"x": 8, "y": 68, "c":0}, {"x": 8, "y": 16, "c":1},
        {"x": 9, "y": 49, "c":0}, {"x": 9, "y": 25, "c":1}
      ]
    }
  ],

  "scales": [
    {
      "name": "x",
      "type": "point",
      "range": "width",
      "domain": {"data": "table", "field": "x"}
    },
    {
      "name": "y",
      "type": "linear",
      "range": "height",
      "nice": true,
      "zero": true,
      "domain": {"data": "table", "field": "y"}
    },
    {
      "name": "color",
      "type": "ordinal",
      "range": "category",
      "domain": {"data": "table", "field": "c"}
    }
  ],

  "axes": [
    {"orient": "bottom", "scale": "x"},
    {"orient": "left", "scale": "y"}
  ],

  "marks": [
    {
      "type": "group",
      "from": {
        "facet": {
          "name": "series",
          "data": "table",
          "groupby": "c"
        }
      },
      "marks": [
        {
          "type": "line",
          "from": {"data": "series"},
          "encode": {
            "enter": {
              "x": {"scale": "x", "field": "x"},
              "y": {"scale": "y", "field": "y"},
              "stroke": {"scale": "color", "field": "c"},
              "strokeWidth": {"value": 2}
            },
            "update": {
              "interpolate": {"signal": "interpolate"},
              "fillOpacity": {"value": 1}
            },
            "hover": {
              "fillOpacity": {"value": 0.5}
            }
          }
        }
      ]
    }
  ]
}