Chart.js/docs/01-Scales.md

title	anchor
Getting started	scales

###Scales

Scales in v2.0 of Chart.js are significantly more powerful, but also different than those of v1.0.

• Multiple x & y axes are now supported.
• A built-in label auto-skip feature now detects would-be overlapping ticks and labels and removes every nth label to keep things displaying normally.
• Scale labels

Every scale extends a core scale class with the following options:

Name	Type	Default	Description
type	String	Chart specific.	Type of scale being employed. Custom scales can be created. Options: "category", "linear", "logarithmic", "time", "radialLinear"
display	Boolean	true	If true, show the scale including gridlines, ticks, and labels. Overrides gridLines.show, scaleLabel.show, and ticks.show.
gridLines	Array	-	Options for the grid lines that run perpendicular to the axis.
gridLines.show	Boolean	true	If true, show the grid lines.
gridLines.color	Color	"rgba(0, 0, 0, 0.1)"	Color of the grid lines.
gridLines.lineWidth	Number	1	Width of the grid lines in number of pixels.
gridLines.drawOnChartArea	Boolean	true	If true, draw lines on the chart area inside the axis lines.
gridLines.drawTicks	Boolean	true	If true, draw lines beside the ticks in the axis area beside the chart.
gridLines.zeroLineWidth	Number	1	Width of the grid line for the first index (index 0).
gridLines.zeroLineColor	Color	"rgba(0, 0, 0, 0.25)"	Color of the grid line for the first index (index 0).
gridLines.offsetGridLines	Boolean	false	If true, offset labels from grid lines.
scaleLabel	Array		Label for the entire axis.
scaleLabel.show	Boolean	false	If true, show the scale label.
scaleLabel.labelString	String	""	The text for the label. (i.e. "# of People", "Response Choices")
scaleLabel.fontColor	Color	"#666"	Font color for the scale label.
scaleLabel.fontFamily	String	"Helvetica Neue"	Font family for the scale label, follows CSS font-family options.
scaleLabel.fontSize	Number	12	Font size for the scale label.
scaleLabel.fontStyle	String	"normal"	Font style for the scale label, follows CSS font-style options (i.e. normal, italic, oblique, initial, inherit).
ticks	Array		Settings for the labels that run along the axis.
ticks.beginAtZero	Boolean	false	If true the scale will be begin at 0, if false the ticks will begin at your smallest data value.
ticks.fontColor	Color	"#666"	Font color for the tick labels.
ticks.fontFamily	String	"Helvetica Neue"	Font family for the tick labels, follows CSS font-family options.
ticks.fontSize	Number	12	Font size for the tick labels.
ticks.fontStyle	String	"normal"	Font style for the tick labels, follows CSS font-style options (i.e. normal, italic, oblique, initial, inherit).
ticks.maxRotation	Number	90	Maximum rotation for tick labels when rotating to condense labels. Note: Rotation doesn't occur until necessary. Note: Only applicable to horizontal scales.
ticks.minRotation	Number	20	currently not-implemented Minimum rotation for tick labels when condensing is necessary. Note: Only applicable to horizontal scales.
ticks.padding	Number	10	Padding between the tick label and the axis. Note: Only applicable to horizontal scales.
ticks.mirror	Boolean	false	Flips tick labels around axis, displaying the labels inside the chart instead of outside. Note: Only applicable to vertical scales.
ticks.reverse	Boolean	false	Reverses order of tick labels.
ticks.show	Boolean	true	If true, show the ticks.
ticks.suggestedMin	Number	-	User defined minimum number for the scale, overrides minimum value except for if it is higher than the minimum value.
ticks.suggestedMax	Number	-	User defined maximum number for the scale, overrides maximum value except for if it is lower than the maximum value.
ticks.callback	Function	function(value) { return '' + value; }	Returns the string representation of the tick value as it should be displayed on the chart.

The userCallback method may be used for advanced tick customization. The following callback would display every label in scientific notation

{
    scales: {
        xAxes: [{
            ticks: {
                // Return an empty string to draw the tick line but hide the tick label
                // Return `null` or `undefined` to hide the tick line entirely
               	userCallback: function(value, index, values) {
    				return value.toExponential();
    			}
            }
        }]
    }
}

Category Scale

The category scale will be familiar to those who have used v1.0. Labels are drawn in from the labels array included in the chart data.

The category scale extends the core scale class with the following tick template:

{
	position: "bottom",
}

Linear Scale

The linear scale can be used to display numerical data. It can be placed on either the x or y axis. The scatter chart type automatically configures a line chart to use one of these scales for the x axis.

The linear scale extends the core scale class with the following tick template:

{
	position: "left",
}

It also provides additional configuration options:

Name	Type	Default	Description
ticks.fixedStepSize	Number	-	User defined fixed step size for the scale. If set, the scale ticks will be enumerated by multiple of fixedStepSize, having one tick per increment. If not set, the ticks are labeled automatically using the nice numbers algorithm. Works well with suggestedMin and suggestedMax.

Logarithmic Scale

The logarithmic scale is used to display logarithmic data of course. It can be placed on either the x or y axis.

The log scale extends the core scale class with the following tick template:

{
	position: "left",
	ticks: {
		template: "<%var remain = value / (Math.pow(10, Math.floor(Chart.helpers.log10(value))));if (remain === 1 || remain === 2 || remain === 5) {%><%=value.toExponential()%><%} else {%><%= null %><%}%>",
	}
}

Time Scale

The time scale is used to display times and dates. It can be placed on the x axis. When building its ticks, it will automatically calculate the most comfortable unit base on the size of the scale.

The time scale extends the core scale class with the following tick template:

{
	position: "bottom",
	time: {
		// string/callback - By default, date objects are expected. You may use a pattern string from http://momentjs.com/docs/#/parsing/string-format/ to parse a time string format, or use a callback function that is passed the label, and must return a moment() instance.
		format: false,
		// string - By default, unit will automatically be detected.  Override with 'week', 'month', 'year', etc. (see supported time measurements)
		unit: false,
		// string - By default, no rounding is applied.  To round, set to a supported time unit eg. 'week', 'month', 'year', etc.
		round: false,
		// string - By default, is set to the detected (or manually overridden) time unit's `display` property (see supported time measurements).  To override, use a pattern string from http://momentjs.com/docs/#/displaying/format/
		displayFormat: false
	},
}

The following time measurements are supported:

{
	'millisecond': {
		display: 'SSS [ms]', // 002 ms
		maxStep: 1000,
	},
	'second': {
		display: 'h:mm:ss a', // 11:20:01 AM
		maxStep: 60,
	},
	'minute': {
		display: 'h:mm:ss a', // 11:20:01 AM
		maxStep: 60,
	},
	'hour': {
		display: 'MMM D, hA', // Sept 4, 5PM
		maxStep: 24,
	},
	'day': {
		display: 'll', // Sep 4 2015
		maxStep: 7,
	},
	'week': {
		display: 'll', // Week 46, or maybe "[W]WW - YYYY" ?
		maxStep: 4.3333,
	},
	'month': {
		display: 'MMM YYYY', // Sept 2015
		maxStep: 12,
	},
	'quarter': {
		display: '[Q]Q - YYYY', // Q3
		maxStep: 4,
	},
	'year': {
		display: 'YYYY', // 2015
		maxStep: false,
	},
}

Radial Linear Scale

The radial linear scale is used specifically for the radar chart type.

The radial linear scale extends the core scale class with the following tick template:

{
	animate: true,
	lineArc: false,
	position: "chartArea",

	angleLines: {
		show: true,
		color: "rgba(0, 0, 0, 0.1)",
		lineWidth: 1
	},

	// label settings
	ticks: {
		//Boolean - Show a backdrop to the scale label
		showLabelBackdrop: true,

		//String - The colour of the label backdrop
		backdropColor: "rgba(255,255,255,0.75)",

		//Number - The backdrop padding above & below the label in pixels
		backdropPaddingY: 2,

		//Number - The backdrop padding to the side of the label in pixels
		backdropPaddingX: 2,

		//Number - Limit the maximum number of ticks
		maxTicksLimit: 11,
	},

	pointLabels: {
		//String - Point label font declaration
		fontFamily: "'Arial'",

		//String - Point label font weight
		fontStyle: "normal",

		//Number - Point label font size in pixels
		fontSize: 10,

		//String - Point label font colour
		fontColor: "#666",
	},
}