G2

Overview

density is a chart type used to visualize the probability density distribution of continuous variables. Through kernel density estimation (Kernel Density Estimation, KDE), it transforms discrete data points into smooth continuous probability density curves, intuitively reflecting data concentration trends, distribution patterns, and outliers.

The core goal of density is to extract overall distribution patterns from scatter or point cloud data and map density information to a continuous area chart or gradient effect. This chart type is commonly used to analyze aggregation areas of large amounts of data points, data concentration hotspots, or probability density of data distribution, such as representing population density in geographic visualization, or showing regional trading frequency in analysis.

import { Chart } from '@antv/g2';

const chart = new Chart({
  container: 'container',
});

chart.options({
  type: 'density', // Set chart type as density plot
  data: {
    type: 'fetch', // Specify data type as network fetch
    value: 'https://assets.antv.antgroup.com/g2/species.json', // Set data URL address
    transform: [
      {
        type: 'kde', // Use Kernel Density Estimation (KDE) for data transformation
        field: 'y', // Specify KDE calculation field as 'y'
        groupBy: ['x', 'species'], // Group data by 'x' and 'species' fields
      },
    ],
  },
  encode: {
    x: 'x', // Map 'x' field to x-axis
    y: 'y', // Map 'y' field to y-axis
    color: 'species', // Map 'species' field to color
    size: 'size', // Map 'size' field to graphic size
    series: 'species', // Map 'species' field to series
  },

  tooltip: false, // Disable chart tooltip functionality
});

chart.render();

For more examples, please check the Chart Examples - Violin Plot page.

Configuration Options

Property	Description	Type	Default Value	Required
coordinate	Configure `density` chart coordinate system, supports properties: `cartesian` \| `polar`	coordinate	`'cartesian'`
encode	Configure `density` mark visual channels, including `x`, `y`, `color`, `size`, etc., used to specify relationships between visual element properties and data	encode	-	✓
scale	Configure `density` mark graphic scaling, including `x`, `y`, `series`, `size`, etc.	scale	-
style	Configure `density` graphic style	style	-

coordinate

coordinate is the core system in data visualization that defines how data maps to graphic space. It determines how data transforms from "numerical domain" to "visual position". Coordinate systems reshape the visual expression of density distribution through different spatial transformation rules.

Coordinate System	Type	Chart
Cartesian	`'cartesian'`	Density plot, etc.
Polar	`'polar'`	Polar violin plot, etc.

(() => {
  const coordinateMap = [
    {
      coordinate: 'cartesian',
      label: 'Cartesian Coordinate System',
    },
    {
      coordinate: 'polar',
      label: 'Polar Coordinate System',
    },
  ];

  const chart = new G2.Chart();

  chart.options({
    type: 'density',
    data: {
      type: 'fetch',
      value: 'https://assets.antv.antgroup.com/g2/species.json',
      transform: [
        {
          type: 'kde',
          field: 'y',
          groupBy: ['x', 'species'],
        },
      ],
    },
    encode: {
      x: 'x',
      y: 'y',
      color: 'species',
      size: 'size',
      series: 'species',
    },
    coordinate: { type: coordinateMap[0].coordinate },
    tooltip: false,
  });

  const handleSetCoordinate = (coordinate) => {
    // Set selected coordinate system
    chart.coordinate({
      type: coordinate,
    });
    chart.render(); // Re-render chart
  };

  // Insert Encode-Color selector
  const selectorContainer = document.createElement('div');
  selectorContainer.textContent = 'Select Coordinate System ';
  const selector = document.createElement('select');
  selector.innerHTML = coordinateMap.map(
    (coordinate, index) =>
      `<option value="${coordinate.coordinate}" ${
        index === 0 ? 'selected' : ''
      }>${coordinate.label}</option>`,
  );
  selector.onchange = (e) => {
    handleSetCoordinate(e.target.value);
  };
  selectorContainer.appendChild(selector);
  const node = chart.getContainer();
  node.insertBefore(selectorContainer, node.childNodes[0]);

  chart.render();

  return node;
})();

For more coordinate configuration, please check the coordinate introduction page.

encode

Configure density mark visual channels, an important configuration that defines the mapping relationships between data fields and visual properties, determining how data transforms into visual representation.

Property	Description	Type	Default Value	Required
x	Bind the `x` property channel of `density` mark, usually a time or ordered categorical field in `data`	encode	-	✓
y	Bind the `y` property channel of `density` mark, usually a numerical or array field in `data`	encode	-	✓
color	Bind the `color` property channel of `density` mark. If a data field is mapped to the color channel, data will be grouped and split into multiple areas with different colors	encode	-
size	Bind the `size` property channel of `density` mark, used to map data fields to the size property of graphic elements, enhancing data distribution comparison dimensions and information density by adjusting density curve line thickness or filled area visual proportions	encode	-	✓
series	Bind the `series` property channel of `density` mark, used to map data grouping fields to chart series or categories, classifying data according to a field and generating independent graphic representations for each category	encode	-	✓

For more encode configuration, please check the encode introduction page.

scale

scale is used to define how data maps to visual properties (such as color, size, shape, etc.). In density usage scenarios, the common role of scale is to provide mapping rules for each visual channel (such as color, size, position, etc.), enabling data points to be accurately presented.

Property	Description	Type	Default Value
x	Define mapping rules from data fields to X-axis visual positions	scale	`{type: 'band'}`
series	Control mapping rules from categorical fields (series encoding) to visual properties (such as color, line type, symbols)	scale	`{type: 'band'}`
size	Map data fields to size properties of visual elements (such as density curve width, point area, or region height)	scale	`{type: 'identity'}`

For more scale configuration, please check the scale introduction page.

style

style is used to set the appearance style of chart elements, including fill color, border style, shadow effects, etc.

Property	Description	Type	Default Value
fill	Fill color of the graphic	`string` \| `Function<string>`	-
fillOpacity	Fill opacity of the graphic	`number` \| `Function<number>`	-
stroke	Stroke of the graphic	`string` \| `Function<string>`	-
strokeOpacity	Stroke opacity	`number` \| `Function<number>`	-
lineWidth	Width of graphic stroke	`number` \| `Function<number>`	-
lineDash	Dashed line configuration for stroke. The first value is the length of each dash segment, the second value is the distance between segments. Setting lineDash to [0, 0] results in no stroke.	`[number,number]` \| `Function<[number, number]>`	-
opacity	Overall opacity of the graphic	`number` \| `Function<number>`	-
shadowColor	Shadow color of the graphic	`string` \| `Function<string>`	-
shadowBlur	Gaussian blur coefficient of graphic shadow	`number` \| `Function<number>`	-
shadowOffsetX	Set horizontal distance of shadow from graphic	`number` \| `Function<number>`	-
shadowOffsetY	Set vertical distance of shadow from graphic	`number` \| `Function<number>`	-
cursor	Mouse cursor style. Same as CSS cursor style, default 'default'.	`string` \| `Function<string>`	`'default'`

For more style configuration, please check the style introduction page.

Try it out: