# Axes

Axes are an integral part of a chart. They are used to determine how data maps to a pixel value on the chart. In a cartesian chart, there is 1 or more X axis and 1 or more Y axis to map points onto the 2 dimensional canvas. These axes are know as ['cartesian axes'](./cartesian/README.md#cartesian-axes).

In a radial chart, such as a radar chart or a polar area chart, there is a single axis that maps points in the angular and radial directions. These are known as ['radial axes'](./radial/README.md#radial-axes).

Scales in Chart.js >v2.0 are significantly more powerful, but also different than those of v1.0.
* Multiple X & Y axes are supported.
* A built-in label auto-skip feature detects would-be overlapping ticks and labels and removes every nth label to keep things displaying normally.
* Scale titles are supported.
* New scale types can be extended without writing an entirely new chart type.

## Common Configuration

The following properties are common to all axes provided by Chart.js.

| Name | Type | Default | Description
| ---- | ---- | ------- | -----------
| `display` | <code>boolean&#124;string</code> | `true` | Controls the axis global visibility (visible when `true`, hidden when `false`). When `display: 'auto'`, the axis is visible only if at least one associated dataset is visible.
| `callbacks` | `object` | | Callback functions to hook into the axis lifecycle. [more...](#callbacks)
| `weight` | `number` | `0` | The weight used to sort the axis. Higher weights are further away from the chart area.

### Callbacks
There are a number of config callbacks that can be used to change parameters in the scale at different points in the update process.

| Name | Arguments | Description
| ---- | --------- | -----------
| `beforeUpdate` | `axis` | Callback called before the update process starts.
| `beforeSetDimensions` | `axis` | Callback that runs before dimensions are set.
| `afterSetDimensions` | `axis` | Callback that runs after dimensions are set.
| `beforeDataLimits` | `axis` | Callback that runs before data limits are determined.
| `afterDataLimits` | `axis` | Callback that runs after data limits are determined.
| `beforeBuildTicks` | `axis` | Callback that runs before ticks are created.
| `afterBuildTicks` | `axis`, `ticks` | Callback that runs after ticks are created. Useful for filtering ticks. Should return the filtered ticks.
| `beforeTickToLabelConversion` | `axis` | Callback that runs before ticks are converted into strings.
| `afterTickToLabelConversion` | `axis` | Callback that runs after ticks are converted into strings.
| `beforeCalculateTickRotation` | `axis` | Callback that runs before tick rotation is determined.
| `afterCalculateTickRotation` | `axis` | Callback that runs after tick rotation is determined.
| `beforeFit` | `axis` | Callback that runs before the scale fits to the canvas.
| `afterFit` | `axis` | Callback that runs after the scale fits to the canvas.
| `afterUpdate` | `axis` | Callback that runs at the end of the update process.

### Updating Axis Defaults

The default configuration for a scale can be easily changed using the scale service. All you need to do is to pass in a partial configuration that will be merged with the current scale default configuration to form the new default.

For example, to set the minimum value of 0 for all linear scales, you would do the following. Any linear scales created after this time would now have a minimum of 0.

```javascript
Chart.scaleService.updateScaleDefaults('linear', {
    ticks: {
        min: 0
    }
});
```

## Creating New Axes
To create a new axis, see the [developer docs](../developers/axes.md).
