G2

In G2, the scale is a crucial abstraction for visualization: it maps abstract data to visual data, serving as the bridge between abstract data and visual data. If the encode determines which channels of the mark need to be visualized, then the scale determines how these channels should be visualized.

G2 internally infers the type, domain, and range of the scale based on the data type and the type of the mark, but you can also specify the corresponding configuration. The scale can be configured at the mark level:

({
  type: 'interval',
  scale: {
    x: { padding: 0.5 },
    y: {
      type: 'log', // specify type
      domain: [10, 100], // specify domain
      range: [0, 1], // specify range
    },
  },
});

// API
// First way
chart
  .interval()
  .scale('x', { padding: 0.5 })
  .scale('y', {
    type: 'log', // specify type
    domain: [10, 100], // specify domain
    range: [0, 1], // specify range
  });

// Second way
chart.interval().scale({
  x: { padding: 0.5 },
  y: {
    type: 'log', // specify type
    domain: [10, 100], // specify domain
    range: [0, 1], // specify range
  },
});

The scale can also be configured at the view level:

({
  type: 'view',
  scale: {
    x: { padding: 0.5 },
    y: {
      type: 'log', // specify type
      domain: [10, 100], // specify domain
      range: [0, 1], // specify range
    },
  },
});

// API form
// First way
chart.scale('x', { padding: 0.5 }).scale('y', {
  type: 'log', // specify type
  domain: [10, 100], // specify domain
  range: [0, 1], // specify range
});

// Second way
chart.scale({
  x: { padding: 0.5 },
  y: {
    type: 'log', // specify type
    domain: [10, 100], // specify domain
    range: [0, 1], // specify range
  },
});

Mark Scale

Every channel of the mark is bound to a scale. This scale transforms the column data bound to the channel from the data range: domain to the visual range: range. Different types of scales are suitable for different types of data and use cases.

Scale Synchronization

The scale of the same channel of the mark in the same view is synchronized by default: it synchronizes the type, domain, and range of the scale, as well as other configurations. This means that all marks in a view will be drawn with the same scale. For example, the LineX mark in the figure below, although it does not have complete data, is still drawn at the accurate position, because the scale is synchronized.

(() => {
  const chart = new G2.Chart();

  chart
    .line()
    .data([
      { year: '1991', value: 3 },
      { year: '1992', value: 4 },
      { year: '1993', value: 3.5 },
      { year: '1994', value: 5 },
      { year: '1995', value: 4.9 },
      { year: '1996', value: 6 },
      { year: '1997', value: 7 },
      { year: '1998', value: 9 },
      { year: '1999', value: 13 },
    ])
    .encode('x', 'year')
    .encode('y', 'value');

  chart.lineX().data(['1996']).style('stroke', 'red').style('strokeWidth', 2);

  chart.render();

  return chart.getContainer();
})();

Scales Out of Sync

If you want to unsynchronized (for example, when drawing a dual-axis chart), you need to set scale.independent to true. The scale that has set this property will not synchronize with any other scale. In the example below, the y-axis of the interval and line will use two different scales, thus generating two different coordinate axes.

(() => {
  const chart = new G2.Chart();

  chart.options({
    type: 'view',
    data: [
      { time: '10:10', call: 4, waiting: 2, people: 2 },
      { time: '10:15', call: 2, waiting: 6, people: 3 },
      { time: '10:20', call: 13, waiting: 2, people: 5 },
      { time: '10:25', call: 9, waiting: 9, people: 1 },
      { time: '10:30', call: 5, waiting: 2, people: 3 },
      { time: '10:35', call: 8, waiting: 2, people: 1 },
      { time: '10:40', call: 13, waiting: 1, people: 2 },
    ],
    children: [
      {
        type: 'interval',
        encode: { x: 'time', y: 'waiting' },
        axis: { y: { title: 'Waiting', titleFill: '#5B8FF9' } },
      },
      {
        type: 'line',
        encode: { x: 'time', y: 'people', shape: 'smooth' },
        scale: { y: { independent: true } }, // Set y-axis scale to unsynchronized
        style: { stroke: '#fdae6b', lineWidth: 2 },
        axis: {
          y: {
            position: 'right',
            grid: null,
            title: 'People',
            titleFill: '#fdae6b',
          },
        },
      },
    ],
  });

  chart.render();

  return chart.getContainer();
})();

If you want to synchronize scales in groups, you can declare scale.key. Scales with the same key will synchronize. For example, the y-axis of Line and Point Mark in the example below will synchronize because the key of both is 'line'.

(() => {
  const chart = new G2.Chart();

  chart.options({
    type: 'view',
    data: [
      { time: '10:10', call: 4, waiting: 2, people: 2 },
      { time: '10:15', call: 2, waiting: 6, people: 3 },
      { time: '10:20', call: 13, waiting: 2, people: 5 },
      { time: '10:25', call: 9, waiting: 9, people: 1 },
      { time: '10:30', call: 5, waiting: 2, people: 3 },
      { time: '10:35', call: 8, waiting: 2, people: 1 },
      { time: '10:40', call: 13, waiting: 1, people: 2 },
    ],
    children: [
      {
        type: 'interval',
        encode: { x: 'time', y: 'waiting' },
        axis: { y: { title: 'Waiting', titleFill: '#5B8FF9' } },
      },
      {
        type: 'line',
        encode: { x: 'time', y: 'people', shape: 'smooth' },
        scale: { y: { key: 'line' } }, // Set key to 'line'
        style: { stroke: '#fdae6b', lineWidth: 2 },
        axis: {
          y: {
            position: 'right',
            grid: null,
            title: 'People',
            titleFill: '#fdae6b',
          },
        },
      },
      {
        type: 'point',
        encode: { x: 'time', y: 'people' },
        scale: { y: { key: 'line' } }, // Set key to 'line'
        style: { stroke: '#fdae6b', lineWidth: 2 },
      },
    ],
  });

  chart.render();

  return chart.getContainer();
})();

View Scale

The scale can be configured in the view hierarchy and passed to the children specified by the mark. If the channel corresponding to the mark does not set the scale, it is set; otherwise, it has no effect. When not drawing multi-axis charts, the scale can be set at the view hierarchy.

(() => {
  const chart = new G2.Chart();

  chart
    .data([
      { year: '1991', value: 3 },
      { year: '1992', value: 4 },
      { year: '1993', value: 3.5 },
      { year: '1994', value: 5 },
      { year: '1995', value: 4.9 },
      { year: '1996', value: 6 },
      { year: '1997', value: 7 },
      { year: '1998', value: 9 },
      { year: '1999', value: 13 },
    ])
    .encode('x', 'year')
    .encode('y', 'value')
    .scale('y', { nice: true }); // Scale setting at the view hierarchy

  chart.line();

  chart.point();

  chart.render();

  return chart.getContainer();
})();

Common Scales

Common scales are divided into three major categories:

Continuous scale
Discrete scale
Discretizing scale

Continuous Scale

The first type of scale is the continuous scale, mainly used for continuous data. Common continuous scales include Linear, Time, Log, etc. For example, the x and y channels in the scatter plot below use the linear scale.

(() => {
  const chart = new G2.Chart();

  chart
    .point()
    .data({
      type: 'fetch',
      value:
        'https://gw.alipayobjects.com/os/antvdemo/assets/data/scatter.json',
    })
    .encode('x', 'weight') // weight is continuous data
    .encode('y', 'height') // height is continuous data
    .encode('color', 'gender');

  chart.render();

  return chart.getContainer();
})();

Ordinal Scale

The second type of scale is the ordinal scale, mainly used for discrete data. Common ordinal scales include ordinal, point, etc. For example, the color channel in the bar chart below uses the ordinal scale.

(() => {
  const chart = new G2.Chart();

  chart
    .interval()
    .data([
      { genre: 'Sports', sold: 275 },
      { genre: 'Strategy', sold: 115 },
      { genre: 'Action', sold: 120 },
      { genre: 'Shooter', sold: 350 },
      { genre: 'Other', sold: 150 },
    ])
    .encode('x', 'genre')
    .encode('y', 'sold')
    .encode('color', 'genre') // genre is discrete data
    .scale('color', {
      // Specify the color after mapping
      range: ['#1f77b4', '#ff7f0e', '#2ca02c', '#d62728', '#c564be'],
    });

  chart.render();

  return chart.getContainer();
})();

Discretizing Scale

The third type of scale is the discretizing scale, mainly used for continuous data, which will be discretized and then mapped, such as threshold, quantize, etc. The color channel below uses the quantile scale.

(() => {
  const chart = new G2.Chart({
    
    height: 240,
  });

  chart
    .cell()
    .data({
      type: 'fetch',
      value:
        'https://gw.alipayobjects.com/os/bmw-prod/89c20fe8-0c6f-46c8-b36b-4cb653dba8ed.json',
      transform: [{ type: 'map', callback: (d) => ({ salary: d }) }],
    })
    .scale('color', {
      type: 'quantile',
      // divided into three groups, each group corresponds to the following color
      range: ['#eee', 'pink', 'red'],
    })
    .encode('y', (_, i) => (i % 5) + 1)
    .encode('x', (_, i) => ((i / 5) | 0) + 1)
    .encode('color', 'salary') // is continuous data, the scale groups data by quantile
    .style('stroke', '#000')
    .style('inset', 2);

  chart.render();

  return chart.getContainer();
})();

overview