The horizontal (X) and vertical (Y) lines in cartesian charts are referred to as chart axes, and they serve to illustrate the relationships between data points on the graph. This section discusses the different axis types.
Category Copy Link
A category axis is used to display distinct categories or groups of data in a chart.
The category axis shows discrete categories or groups of data, unlike the Number or Time axes which use a continuous scale. For instance, in a bar chart of sales per product, the category axis shows the products as different groups, and the number axis displays the corresponding sale value for each group.
If no axes are supplied, a category axis will be used as the x-axis by default. However, it can also be explicitly configured as shown below:
axes: [
{
type: 'category',
position: 'bottom',
},
],
The category axis will attempt to render an Axis Label, Grid Line and Tick for each category with even spacing.
For a full list of configuration options see Category Axis Options.
Grouped Category Copy Link
A grouped category axis is similar to the regular category axis, with the additional ability to display nested categories or hierarchical groups of data.
To use a grouped category axis, the xKey needs to reference an array of strings, with each string representing a level in the hierarchy.
For example, to create the above example comparing Olympic medal counts by hierarchical location, the data must include an array with the regions, countries, and cities.
data: [
{ location: ['Europe', 'United Kingdom', 'London'], gold: 27, silver: 23, bronze: 17 },
{ location: ['Europe', 'United Kingdom', 'Manchester'], gold: 12, silver: 8, bronze: 10 },
{ location: ['Asia', 'China', 'Beijing'], gold: 38, silver: 32, bronze: 18 },
{ location: ['Asia', 'China', 'Shanghai'], gold: 20, silver: 15, bronze: 12 },
{ location: ['Asia', 'Japan', 'Tokyo'], gold: 27, silver: 14, bronze: 17 },
{ location: ['North America', 'United States', 'Los Angeles'], gold: 46, silver: 37, bronze: 38 },
{ location: ['North America', 'Canada', 'Toronto'], gold: 8, silver: 6, bronze: 10 },
],
The grouped category axis will render Axis Labels, Grid Lines, and Ticks for each level in the hierarchy, aligning them to visually represent the nested relationships between categories.
Ticks and labels for all levels inherit styles from the axis options by default. To style each level differently, use the depthOptions array, where each entry corresponds to a hierarchy level, starting at the leaf level.
type: 'grouped-category',
depthOptions: [
{}, // Skip depth 0 - the nearest to the axis, no unique styles.
{ label: { fontWeight: 'bold' } }, // depth 1
{ label: { fontSize: 10 } }, //depth 2
],
Number Copy Link
A number axis is used to display continuous numerical values in a chart.
The number axis displays continuous numerical values, unlike the Category axis which displays discrete categories or groups of data. This means that while categories are spaced out evenly, the distance between values in a number axis will depend on their magnitude.
Instead of using an Axis Interval with one item per value, the number axis will determine the range of all values, round it up and try to segment the rounded range with evenly spaced intervals.
If no axes are supplied, a number axis will be used as the y-axis by default. However, it can also be explicitly configured as shown below:
axes: [
{
type: 'number',
position: 'left',
},
],
For a full list of configuration options see Number Axis Options.
Log Copy Link
If the range of values is very wide, the log axis can be used instead of the number axis. For example, because the number axis uses a linear scale, same changes in magnitude result in the same pixel distance.
The log axis uses a log scale, where same percentage changes in magnitude result in the same pixel distance. In other words, the pixel distance between 10 and 100, and 100 and 1000 will be the same because both ranges represent the same percentage increase. Whereas, if the number axis was used, the second distance would be 10 times larger than the first.
The above property of the log axis can also be useful in financial charts. For example, if your rate of return on an investment stays consistent over time, the investment value chart will look like a straight line.
By default, if the data domain has 5 or more orders of magnitude, the log axis attempts to render 5 ticks. Otherwise, 10 ticks (the logarithm base) is rendered per order of magnitude. For example a data domain of [1, 100] with 2 orders of magnitude, will show 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100.
Depending on the data domain and chart size, using a larger value for the tick: { minSpacing: xxx } config might be necessary to reduce the number of ticks.
{
type: 'log',
position: 'left',
minSpacing: 200,
}
The log axis uses the common logarithm (base 10) by default. The base config allows you to change the base to any number you like, for example Math.E for natural or 2 for binary logarithms:
{
type: 'log',
position: 'left',
base: 2,
}
For a full list of configuration options see Log Axis Options.
These configurations above are demonstrated in the following example:
The domain of a log axis should be strictly positive or strictly negative (because there's no power you can raise a number to that will yield zero). For that reason, any non-conforming domain will be clipped to conformity. For example, [0, 10] will be clipped to [1, 10]. If the data domain crosses 0, for example [-10, 5], no data will be rendered. It is often desirable to set the min or max property of the axis manually. In this case it can be max: -1.
Time Copy Link
There are three methods of displaying time along an axis.
- Unit Time Axis - Each 'unit' has a dedicated band within the domain.
- Ordinal Time Axis - Only provided values are shown, with missing values omitted.
- Continuous Time Axis - Data is shown on a continuous scale.
The difference between a Unit Time Axis, an Ordinal Time Axis, and a continuous Continuous Time Axis is demonstrated in the following example:
For more detail on time axes, see the Time Axes page.
API Reference Copy Link
Next Up Copy Link
Continue to the next section to learn about the Axis Intervals.