## README

# d3-scale

Scales are a convenient abstraction for a fundamental task in visualization: mapping a dimension of abstract data to a visual representation. Although most often used for position-encoding quantitative data, such as mapping a measurement in meters to a position in pixels for dots in a scatterplot, scales can represent virtually any visual encoding, such as diverging colors, stroke widths, or symbol size. Scales can also be used with virtually any type of data, such as named categorical data or discrete data that requires sensible breaks.

For continuous quantitative data, you typically want a linear scale. (For time series data, a time scale.) If the distribution calls for it, consider transforming data using a power or log scale. A quantize scale may aid differentiation by rounding continuous data to a fixed set of discrete values; similarly, a quantile scale computes quantiles from a sample population, and a threshold scale allows you to specify arbitrary breaks in continuous data.

For discrete ordinal (ordered) or categorical (unordered) data, an ordinal scale specifies an explicit mapping from a set of data values to a corresponding set of visual attributes (such as colors). The related band and point scales are useful for position-encoding ordinal data, such as bars in a bar chart or dots in an categorical scatterplot.

This repository does not provide color schemes; see d3-scale-chromatic for color schemes designed to work with d3-scale.

Scales have no intrinsic visual representation. However, most scales can generate and format ticks for reference marks to aid in the construction of axes.

For a longer introduction, see these recommended tutorials:

Introducing d3-scale by Mike Bostock

Chapter 7. Scales of

*Interactive Data Visualization for the Web*by Scott Murrayd3: scales, and color. by Jérôme Cukier

## Installing

If you use npm, `npm install d3-scale`

. You can also download the latest release on GitHub. For vanilla HTML in modern browsers, import d3-scale from Skypack:

```
<script type="module">
import {scaleLinear} from "https://cdn.skypack.dev/d3-scale@4";
const x = scaleLinear();
</script>
```

For legacy environments, you can load d3-scale’s UMD bundle from an npm-based CDN such as jsDelivr; a `d3`

global is exported:

```
<script src="https://cdn.jsdelivr.net/npm/d3-array@3"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-color@3"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-format@3"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-interpolate@3"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-time@3"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-time-format@4"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-scale@4"></script>
<script>
const x = d3.scaleLinear();
</script>
```

(You can omit d3-time and d3-time-format if you’re not using d3.scaleTime or d3.scaleUtc.)

## API Reference

- Continuous (Linear, Power, Log, Identity, Time, Radial)
- Sequential
- Diverging
- Quantize
- Quantile
- Threshold
- Ordinal (Band, Point)

### Continuous Scales

Continuous scales map a continuous, quantitative input domain to a continuous output range. If the range is also numeric, the mapping may be inverted. A continuous scale is not constructed directly; instead, try a linear, power, log, identity, radial, time or sequential color scale.

# *continuous*(*value*) · Source, Examples

Given a *value* from the domain, returns the corresponding value from the range. If the given *value* is outside the domain, and clamping is not enabled, the mapping may be extrapolated such that the returned value is outside the range. For example, to apply a position encoding:

```
var x = d3.scaleLinear()
.domain([10, 130])
.range([0, 960]);
x(20); // 80
x(50); // 320
```

Or to apply a color encoding:

```
var color = d3.scaleLinear()
.domain([10, 100])
.range(["brown", "steelblue"]);
color(20); // "#9a3439"
color(50); // "#7b5167"
```

Or, in shorthand:

```
var x = d3.scaleLinear([10, 130], [0, 960]);
var color = d3.scaleLinear([10, 100], ["brown", "steelblue"]);
```

# *continuous*.**invert**(*value*) · Source, Examples

Given a *value* from the range, returns the corresponding value from the domain. Inversion is useful for interaction, say to determine the data value corresponding to the position of the mouse. For example, to invert a position encoding:

```
var x = d3.scaleLinear()
.domain([10, 130])
.range([0, 960]);
x.invert(80); // 20
x.invert(320); // 50
```

If the given *value* is outside the range, and clamping is not enabled, the mapping may be extrapolated such that the returned value is outside the domain. This method is only supported if the range is numeric. If the range is not numeric, returns NaN.

For a valid value *y* in the range, *continuous*(*continuous*.invert(*y*)) approximately equals *y*; similarly, for a valid value *x* in the domain, *continuous*.invert(*continuous*(*x*)) approximately equals *x*. The scale and its inverse may not be exact due to the limitations of floating point precision.

# *continuous*.**domain**([*domain*]) · Source, Examples

If *domain* is specified, sets the scale’s domain to the specified array of numbers. The array must contain two or more elements. If the elements in the given array are not numbers, they will be coerced to numbers. If *domain* is not specified, returns a copy of the scale’s current domain.

Although continuous scales typically have two values each in their domain and range, specifying more than two values produces a piecewise scale. For example, to create a diverging color scale that interpolates between white and red for negative values, and white and green for positive values, say:

```
var color = d3.scaleLinear()
.domain([-1, 0, 1])
.range(["red", "white", "green"]);
color(-0.5); // "rgb(255, 128, 128)"
color(+0.5); // "rgb(128, 192, 128)"
```

Internally, a piecewise scale performs a binary search for the range interpolator corresponding to the given domain value. Thus, the domain must be in ascending or descending order. If the domain and range have different lengths *N* and *M*, only the first *min(N,M)* elements in each are observed.

# *continuous*.**range**([*range*]) · Source, Examples

If *range* is specified, sets the scale’s range to the specified array of values. The array must contain two or more elements. Unlike the domain, elements in the given array need not be numbers; any value that is supported by the underlying interpolator will work, though note that numeric ranges are required for invert. If *range* is not specified, returns a copy of the scale’s current range. See *continuous*.interpolate for more examples.

# *continuous*.**rangeRound**([*range*]) · Source, Examples

Sets the scale’s *range* to the specified array of values while also setting the scale’s interpolator to interpolateRound. This is a convenience method equivalent to:

```
continuous
.range(range)
.interpolate(d3.interpolateRound);
```

The rounding interpolator is sometimes useful for avoiding antialiasing artifacts, though also consider the shape-rendering “crispEdges” styles. Note that this interpolator can only be used with numeric ranges.

# *continuous*.**clamp**(*clamp*) · Source, Examples

If *clamp* is specified, enables or disables clamping accordingly. If clamping is disabled and the scale is passed a value outside the domain, the scale may return a value outside the range through extrapolation. If clamping is enabled, the return value of the scale is always within the scale’s range. Clamping similarly applies to *continuous*.invert. For example:

```
var x = d3.scaleLinear()
.domain([10, 130])
.range([0, 960]);
x(-10); // -160, outside range
x.invert(-160); // -10, outside domain
x.clamp(true);
x(-10); // 0, clamped to range
x.invert(-160); // 10, clamped to domain
```

If *clamp* is not specified, returns whether or not the scale currently clamps values to within the range.

# *continuous*.**unknown**([*value*]) · Source, Examples

If *value* is specified, sets the output value of the scale for undefined (or NaN) input values and returns this scale. If *value* is not specified, returns the current unknown value, which defaults to undefined.

# *continuous*.**interpolate**(*interpolate*) · Source, Examples

If *interpolate* is specified, sets the scale’s range interpolator factory. This interpolator factory is used to create interpolators for each adjacent pair of values from the range; these interpolators then map a normalized domain parameter *t* in [0, 1] to the corresponding value in the range. If *factory* is not specified, returns the scale’s current interpolator factory, which defaults to d3.interpolate. See d3-interpolate for more interpolators.

For example, consider a diverging color scale with three colors in the range:

```
var color = d3.scaleLinear()
.domain([-100, 0, +100])
.range(["red", "white", "green"]);
```

Two interpolators are created internally by the scale, equivalent to:

```
var i0 = d3.interpolate("red", "white"),
i1 = d3.interpolate("white", "green");
```

A common reason to specify a custom interpolator is to change the color space of interpolation. For example, to use HCL:

```
var color = d3.scaleLinear()
.domain([10, 100])
.range(["brown", "steelblue"])
.interpolate(d3.interpolateHcl);
```

Or for Cubehelix with a custom gamma:

```
var color = d3.scaleLinear()
.domain([10, 100])
.range(["brown", "steelblue"])
.interpolate(d3.interpolateCubehelix.gamma(3));
```

Note: the default interpolator **may reuse return values**. For example, if the range values are objects, then the value interpolator always returns the same object, modifying it in-place. If the scale is used to set an attribute or style, this is typically acceptable (and desirable for performance); however, if you need to store the scale’s return value, you must specify your own interpolator or make a copy as appropriate.

# *continuous*.**ticks**([*count*])

Returns approximately *count* representative values from the scale’s domain. If *count* is not specified, it defaults to 10. The returned tick values are uniformly spaced, have human-readable values (such as multiples of powers of 10), and are guaranteed to be within the extent of the domain. Ticks are often used to display reference lines, or tick marks, in conjunction with the visualized data. The specified *count* is only a hint; the scale may return more or fewer values depending on the domain. See also d3-array’s ticks.

# *continuous*.**tickFormat**([*count*[, *specifier*]]) · Source, Examples

Returns a number format function suitable for displaying a tick value, automatically computing the appropriate precision based on the fixed interval between tick values. The specified *count* should have the same value as the count that is used to generate the tick values.

An optional *specifier* allows a custom format where the precision of the format is automatically set by the scale as appropriate for the tick interval. For example, to format percentage change, you might say:

```
var x = d3.scaleLinear()
.domain([-1, 1])
.range([0, 960]);
var ticks = x.ticks(5),
tickFormat = x.tickFormat(5, "+%");
ticks.map(tickFormat); // ["-100%", "-50%", "+0%", "+50%", "+100%"]
```

If *specifier* uses the format type `s`

, the scale will return a SI-prefix format based on the largest value in the domain. If the *specifier* already specifies a precision, this method is equivalent to *locale*.format.

See also d3.tickFormat.

# *continuous*.**nice**([*count*]) · Source, Examples

Extends the domain so that it starts and ends on nice round values. This method typically modifies the scale’s domain, and may only extend the bounds to the nearest round value. An optional tick *count* argument allows greater control over the step size used to extend the bounds, guaranteeing that the returned ticks will exactly cover the domain. Nicing is useful if the domain is computed from data, say using extent, and may be irregular. For example, for a domain of [0.201479…, 0.996679…], a nice domain might be [0.2, 1.0]. If the domain has more than two values, nicing the domain only affects the first and last value. See also d3-array’s tickStep.

Nicing a scale only modifies the current domain; it does not automatically nice domains that are subsequently set using *continuous*.domain. You must re-nice the scale after setting the new domain, if desired.

# *continuous*.**copy**() · Source, Examples

Returns an exact copy of this scale. Changes to this scale will not affect the returned scale, and vice versa.

# d3.**tickFormat**(*start*, *stop*, *count*[, *specifier*]) · Source, Examples

Returns a number format function suitable for displaying a tick value, automatically computing the appropriate precision based on the fixed interval between tick values, as determined by d3.tickStep.

An optional *specifier* allows a custom format where the precision of the format is automatically set by the scale as appropriate for the tick interval. For example, to format percentage change, you might say:

```
var tickFormat = d3.tickFormat(-1, 1, 5, "+%");
tickFormat(-0.5); // "-50%"
```

If *specifier* uses the format type `s`

, the scale will return a SI-prefix format based on the larger absolute value of *start* and *stop*. If the *specifier* already specifies a precision, this method is equivalent to *locale*.format.

#### Linear Scales

# d3.**scaleLinear**([[*domain*, ]*range*]) · Source, Examples

Constructs a new continuous scale with the specified domain and range, the default interpolator and clamping disabled. If either *domain* or *range* are not specified, each defaults to [0, 1]. Linear scales are a good default choice for continuous quantitative data because they preserve proportional differences. Each range value *y* can be expressed as a function of the domain value *x*: *y* = *mx* + *b*.

#### Power Scales

Power scales are similar to linear scales, except an exponential transform is applied to the input domain value before the output range value is computed. Each range value *y* can be expressed as a function of the domain value *x*: *y* = *mx^k* + *b*, where *k* is the exponent value. Power scales also support negative domain values, in which case the input value and the resulting output value are multiplied by -1.

# d3.**scalePow**([[*domain*, ]*range*]) · Source, Examples

Constructs a new continuous scale with the specified domain and range, the exponent 1, the default interpolator and clamping disabled. If either *domain* or *range* are not specified, each defaults to [0, 1]. (Note that this is effectively a linear scale until you set a different exponent.)

# *pow*(*value*) · Source, Examples

See *continuous*.

# *pow*.**invert**(*value*) · Source, Examples

See *continuous*.invert.

# *pow*.**exponent**([*exponent*]) · Source, Examples

If *exponent* is specified, sets the current exponent to the given numeric value. If *exponent* is not specified, returns the current exponent, which defaults to 1. (Note that this is effectively a linear scale until you set a different exponent.)

# *pow*.**domain**([*domain*]) · Source, Examples

See *continuous*.domain.

# *pow*.**range**([*range*]) · Source, Examples

See *continuous*.range.

# *pow*.**rangeRound**([*range*]) · Source, Examples

# *pow*.**clamp**(*clamp*) · Source, Examples

See *continuous*.clamp.

# *pow*.**interpolate**(*interpolate*) · Source, Examples

# *pow*.**ticks**([*count*]) · Source, Examples

See *continuous*.ticks.

# *pow*.**tickFormat**([*count*[, *specifier*]]) · Source, Examples

# *pow*.**nice**([*count*]) · Source, Examples

See *continuous*.nice.

# *pow*.**copy**() · Source, Examples

See *continuous*.copy.

# d3.**scaleSqrt**([[*domain*, ]*range*]) · Source, Examples

Constructs a new continuous power scale with the specified domain and range, the exponent 0.5, the default interpolator and clamping disabled. If either *domain* or *range* are not specified, each defaults to [0, 1]. This is a convenience method equivalent to `d3.scalePow(…).exponent(0.5)`

.

#### Log Scales

Log scales are similar to linear scales, except a logarithmic transform is applied to the input domain value before the output range value is computed. The mapping to the range value *y* can be expressed as a function of the domain value *x*: *y* = *m* log(*x*) + *b*.

As log(0) = -∞, a log scale domain must be **strictly-positive or strictly-negative**; the domain must not include or cross zero. A log scale with a positive domain has a well-defined behavior for positive values, and a log scale with a negative domain has a well-defined behavior for negative values. (For a negative domain, input and output values are implicitly multiplied by -1.) The behavior of the scale is undefined if you pass a negative value to a log scale with a positive domain or vice versa.

# d3.**scaleLog**([[*domain*, ]*range*]) · Source, Examples

Constructs a new continuous scale with the specified domain and range, the base 10, the default interpolator and clamping disabled. If *domain* is not specified, it defaults to [1, 10]. If *range* is not specified, it defaults to [0, 1].

# *log*(*value*) · Source, Examples

See *continuous*.

# *log*.**invert**(*value*) · Source, Examples

See *continuous*.invert.

# *log*.**base**([*base*]) · Source, Examples

If *base* is specified, sets the base for this logarithmic scale to the specified value. If *base* is not specified, returns the current base, which defaults to 10.

# *log*.**domain**([*domain*]) · Source, Examples

See *continuous*.domain.

# *log*.**range**([*range*]) · Source, Examples

See *continuous*.range.

# *log*.**rangeRound**([*range*]) · Source, Examples

# *log*.**clamp**(*clamp*) · Source, Examples

See *continuous*.clamp.

# *log*.**interpolate**(*interpolate*) · Source, Examples

# *log*.**ticks**([*count*]) · Source, Examples

Like *continuous*.ticks, but customized for a log scale. If the base is an integer, the returned ticks are uniformly spaced within each integer power of base; otherwise, one tick per power of base is returned. The returned ticks are guaranteed to be within the extent of the domain. If the orders of magnitude in the domain is greater than *count*, then at most one tick per power is returned. Otherwise, the tick values are unfiltered, but note that you can use *log*.tickFormat to filter the display of tick labels. If *count* is not specified, it defaults to 10.

# *log*.**tickFormat**([*count*[, *specifier*]]) · Source, Examples

Like *continuous*.tickFormat, but customized for a log scale. The specified *count* typically has the same value as the count that is used to generate the tick values. If there are too many ticks, the formatter may return the empty string for some of the tick labels; however, note that the ticks are still shown. To disable filtering, specify a *count* of Infinity. When specifying a count, you may also provide a format *specifier* or format function. For example, to get a tick formatter that will display 20 ticks of a currency, say `log.tickFormat(20, "$,f")`

. If the specifier does not have a defined precision, the precision will be set automatically by the scale, returning the appropriate format. This provides a convenient way of specifying a format whose precision will be automatically set by the scale.

# *log*.**nice**() · Source, Examples

Like *continuous*.nice, except extends the domain to integer powers of base. For example, for a domain of [0.201479…, 0.996679…], and base 10, the nice domain is [0.1, 1]. If the domain has more than two values, nicing the domain only affects the first and last value.

# *log*.**copy**() · Source, Examples

See *continuous*.copy.

#### Symlog Scales

See A bi-symmetric log transformation for wide-range data by Webber for more.

# d3.**scaleSymlog**([[*domain*, ]*range*]) · Source, Examples

Constructs a new continuous scale with the specified domain and range, the constant 1, the default interpolator and clamping disabled. If *domain* is not specified, it defaults to [0, 1]. If *range* is not specified, it defaults to [0, 1].

# *symlog*.**constant**([*constant*]) · Source, Examples

If *constant* is specified, sets the symlog constant to the specified number and returns this scale; otherwise returns the current value of the symlog constant, which defaults to 1. See “A bi-symmetric log transformation for wide-range data” by Webber for more.

#### Identity Scales

Identity scales are a special case of linear scales where the domain and range are identical; the scale and its invert method are thus the identity function. These scales are occasionally useful when working with pixel coordinates, say in conjunction with an axis. Identity scales do not support rangeRound, clamp or interpolate.

# d3.**scaleIdentity**([*range*]) · Source, Examples

Constructs a new identity scale with the specified domain and range. If *range* is not specified, it defaults to [0, 1].

#### Radial Scales

Radial scales are a variant of linear scales where the range is internally squared so that an input value corresponds linearly to the squared output value. These scales are useful when you want the input value to correspond to the area of a graphical mark and the mark is specified by radius, as in a radial bar chart. Radial scales do not support interpolate.

# d3.**scaleRadial**([[*domain*, ]*range*]) · Source, Examples

Constructs a new radial scale with the specified domain and range. If *domain* or *range* is not specified, each defaults to [0, 1].

#### Time Scales

Time scales are a variant of linear scales that have a temporal domain: domain values are coerced to dates rather than numbers, and invert likewise returns a date. Time scales implement ticks based on calendar intervals, taking the pain out of generating axes for temporal domains.

For example, to create a position encoding:

```
var x = d3.scaleTime()
.domain([new Date(2000, 0, 1), new Date(2000, 0, 2)])
.range([0, 960]);
x(new Date(2000, 0, 1, 5)); // 200
x(new Date(2000, 0, 1, 16)); // 640
x.invert(200); // Sat Jan 01 2000 05:00:00 GMT-0800 (PST)
x.invert(640); // Sat Jan 01 2000 16:00:00 GMT-0800 (PST)
```

For a valid value *y* in the range, *time*(*time*.invert(*y*)) equals *y*; similarly, for a valid value *x* in the domain, *time*.invert(*time*(*x*)) equals *x*. The invert method is useful for interaction, say to determine the value in the domain that corresponds to the pixel location under the mouse.

# d3.**scaleTime**([[*domain*, ]*range*]) · Source, Examples

Constructs a new time scale with the specified domain and range, the default interpolator and clamping disabled. If *domain* is not specified, it defaults to [2000-01-01, 2000-01-02]. If *range* is not specified, it defaults to [0, 1].

# *time*(*value*) · Source, Examples

See *continuous*.

# *time*.**invert**(*value*) · Source, Examples

See *continuous*.invert.

# *time*.**domain**([*domain*]) · Source, Examples

See *continuous*.domain.

# *time*.**range**([*range*]) · Source, Examples

See *continuous*.range.

# *time*.**rangeRound**([*range*]) · Source, Examples

# *time*.**clamp**(*clamp*) · Source, Examples

See *continuous*.clamp.

# *time*.**interpolate**(*interpolate*) · Source, Examples

# *time*.**ticks**([*count*]) · Source, Examples

# *time*.**ticks**([*interval*])

Returns representative dates from the scale’s domain. The returned tick values are uniformly-spaced (mostly), have sensible values (such as every day at midnight), and are guaranteed to be within the extent of the domain. Ticks are often used to display reference lines, or tick marks, in conjunction with the visualized data.

An optional *count* may be specified to affect how many ticks are generated. If *count* is not specified, it defaults to 10. The specified *count* is only a hint; the scale may return more or fewer values depending on the domain. For example, to create ten default ticks, say:

```
var x = d3.scaleTime();
x.ticks(10);
// [Sat Jan 01 2000 00:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 03:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 06:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 09:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 12:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 15:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 18:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 21:00:00 GMT-0800 (PST),
// Sun Jan 02 2000 00:00:00 GMT-0800 (PST)]
```

The following time intervals are considered for automatic ticks:

- 1-, 5-, 15- and 30-second.
- 1-, 5-, 15- and 30-minute.
- 1-, 3-, 6- and 12-hour.
- 1- and 2-day.
- 1-week.
- 1- and 3-month.
- 1-year.

In lieu of a *count*, a time *interval* may be explicitly specified. To prune the generated ticks for a given time *interval*, use *interval*.every. For example, to generate ticks at 15-minute intervals:

```
var x = d3.scaleTime()
.domain([new Date(2000, 0, 1, 0), new Date(2000, 0, 1, 2)]);
x.ticks(d3.timeMinute.every(15));
// [Sat Jan 01 2000 00:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 00:15:00 GMT-0800 (PST),
// Sat Jan 01 2000 00:30:00 GMT-0800 (PST),
// Sat Jan 01 2000 00:45:00 GMT-0800 (PST),
// Sat Jan 01 2000 01:00:00 GMT-0800 (PST),
// Sat Jan 01 2000 01:15:00 GMT-0800 (PST),
// Sat Jan 01 2000 01:30:00 GMT-0800 (PST),
// Sat Jan 01 2000 01:45:00 GMT-0800 (PST),
// Sat Jan 01 2000 02:00:00 GMT-0800 (PST)]
```

Alternatively, pass a test function to *interval*.filter:

```
x.ticks(d3.timeMinute.filter(function(d) {
return d.getMinutes() % 15 === 0;
}));
```

Note: in some cases, such as with day ticks, specifying a *step* can result in irregular spacing of ticks because time intervals have varying length.

# *time*.**tickFormat**([*count*[, *specifier*]]) · Source, Examples

# *time*.**tickFormat**([*interval*[, *specifier*]])

Returns a time format function suitable for displaying tick values. The specified *count* or *interval* is currently ignored, but is accepted for consistency with other scales such as *continuous*.tickFormat. If a format *specifier* is specified, this method is equivalent to format. If *specifier* is not specified, the default time format is returned. The default multi-scale time format chooses a human-readable representation based on the specified date as follows:

`%Y`

- for year boundaries, such as`2011`

.`%B`

- for month boundaries, such as`February`

.`%b %d`

- for week boundaries, such as`Feb 06`

.`%a %d`

- for day boundaries, such as`Mon 07`

.`%I %p`

- for hour boundaries, such as`01 AM`

.`%I:%M`

- for minute boundaries, such as`01:23`

.`:%S`

- for second boundaries, such as`:45`

.`.%L`

- milliseconds for all other times, such as`.012`

.

Although somewhat unusual, this default behavior has the benefit of providing both local and global context: for example, formatting a sequence of ticks as [11 PM, Mon 07, 01 AM] reveals information about hours, dates, and day simultaneously, rather than just the hours [11 PM, 12 AM, 01 AM]. See d3-time-format if you’d like to roll your own conditional time format.

# *time*.**nice**([*count*]) · Source, Examples

# *time*.**nice**([*interval*])

Extends the domain so that it starts and ends on nice round values. This method typically modifies the scale’s domain, and may only extend the bounds to the nearest round value. See *continuous*.nice for more.

An optional tick *count* argument allows greater control over the step size used to extend the bounds, guaranteeing that the returned ticks will exactly cover the domain. Alternatively, a time *interval* may be specified to explicitly set the ticks. If an *interval* is specified, an optional *step* may also be specified to skip some ticks. For example, `time.nice(d3.timeSecond.every(10))`

will extend the domain to an even ten seconds (0, 10, 20, *etc.*). See *time*.ticks and *interval*.every for further detail.

Nicing is useful if the domain is computed from data, say using extent, and may be irregular. For example, for a domain of [2009-07-13T00:02, 2009-07-13T23:48], the nice domain is [2009-07-13, 2009-07-14]. If the domain has more than two values, nicing the domain only affects the first and last value.

# *time*.**copy**() · Source, Examples

See *continuous*.copy.

# d3.**scaleUtc**([[*domain*, ]*range*]) · Source, Examples

Equivalent to scaleTime, but the returned time scale operates in Coordinated Universal Time rather than local time.

### Sequential Scales

Sequential scales, like diverging scales, are similar to continuous scales in that they map a continuous, numeric input domain to a continuous output range. However, unlike continuous scales, the input domain and output range of a sequential scale always has exactly two elements, and the output range is typically specified as an interpolator rather than an array of values. These scales do not expose invert and interpolate methods.

# d3.**scaleSequential**([[*domain*, ]*interpolator*]) · Source, Examples

Constructs a new sequential scale with the specified *domain* and *interpolator* function or array. If *domain* is not specified, it defaults to [0, 1]. If *interpolator* is not specified, it defaults to the identity function. When the scale is applied, the interpolator will be invoked with a value typically in the range [0, 1], where 0 represents the minimum value and 1 represents the maximum value. For example, to implement the ill-advised HSL rainbow scale:

```
var rainbow = d3.scaleSequential(function(t) {
return d3.hsl(t * 360, 1, 0.5) + "";
});
```

A more aesthetically-pleasing and perceptually-effective cyclical hue encoding is to use d3.interpolateRainbow:

```
var rainbow = d3.scaleSequential(d3.interpolateRainbow);
```

If *interpolator* is an array, it represents the scale’s two-element output range and is converted to an interpolator function using d3.interpolate.

# *sequential*(*value*) · Source, Examples

See *continuous*.

# *sequential*.**domain**([*domain*]) · Source, Examples

See *continuous*.domain. Note that a sequential scale’s domain must be numeric and must contain exactly two values.

# *sequential*.**clamp**([*clamp*]) · Source, Examples

See *continuous*.clamp.

# *sequential*.**interpolator**([*interpolator*]) · Source, Examples

If *interpolator* is specified, sets the scale’s interpolator to the specified function. If *interpolator* is not specified, returns the scale’s current interpolator.

# *sequential*.**range**([*range*]) · Source, Examples

See *continuous*.range. If *range* is specified, the given two-element array is converted to an interpolator function using d3.interpolate.

# *sequential*.**rangeRound**([*range*]) · Source, Examples

See *continuous*.rangeRound. If *range* is specified, implicitly uses d3.interpolateRound as the interpolator.

# *sequential*.**copy**() · Source, Examples

See *continuous*.copy.

# d3.**scaleSequentialLog**([[*domain*, ]*range*]) · Source, Examples

A sequential scale with a logarithmic transform, analogous to a log scale.

# d3.**scaleSequentialPow**([[*domain*, ]*range*]) · Source, Examples

A sequential scale with an exponential transform, analogous to a power scale.

# d3.**scaleSequentialSqrt**([[*domain*, ]*range*]) · Source, Examples

A sequential scale with a square-root transform, analogous to a d3.scaleSqrt.

# d3.**scaleSequentialSymlog**([[*domain*, ]*range*]) · Source, Examples

A sequential scale with a symmetric logarithmic transform, analogous to a symlog scale.

# d3.**scaleSequentialQuantile**([[*domain*, ]*range*]) · Source, Examples

A sequential scale using a *p*-quantile transform, analogous to a quantile scale.

# *sequentialQuantile*.**quantiles**(*n*) · Source, Examples

Returns an array of *n* + 1 quantiles. For example, if *n* = 4, returns an array of five numbers: the minimum value, the first quartile, the median, the third quartile, and the maximum.

### Diverging Scales

Diverging scales, like sequential scales, are similar to continuous scales in that they map a continuous, numeric input domain to a continuous output range. However, unlike continuous scales, the input domain and output range of a diverging scale always has exactly three elements, and the output range is typically specified as an interpolator rather than an array of values. These scales do not expose invert and interpolate methods.

# d3.**scaleDiverging**([[*domain*, ]*interpolator*]) · Source, Examples

Constructs a new diverging scale with the specified *domain* and *interpolator* function or array. If *domain* is not specified, it defaults to [0, 0.5, 1]. If *interpolator* is not specified, it defaults to the identity function. When the scale is applied, the interpolator will be invoked with a value typically in the range [0, 1], where 0 represents the extreme negative value, 0.5 represents the neutral value, and 1 represents the extreme positive value. For example, using d3.interpolateSpectral:

```
var spectral = d3.scaleDiverging(d3.interpolateSpectral);
```

If *interpolator* is an array, it represents the scale’s three-element output range and is converted to an interpolator function using d3.interpolate and d3.piecewise.

# *diverging*(*value*) · Source, Examples

See *continuous*.

# *diverging*.**domain**([*domain*]) · Source, Examples

See *continuous*.domain. Note that a diverging scale’s domain must be numeric and must contain exactly three values. The default domain is [0, 0.5, 1].

# *diverging*.**clamp**([*clamp*]) · Source, Examples

See *continuous*.clamp.

# *diverging*.**interpolator**([*interpolator*]) · Source, Examples

If *interpolator* is specified, sets the scale’s interpolator to the specified function. If *interpolator* is not specified, returns the scale’s current interpolator.

# *diverging*.**range**([*range*]) · Source, Examples

See *continuous*.range. If *range* is specified, the given three-element array is converted to an interpolator function using d3.interpolate and d3.piecewise.

# *diverging*.**rangeRound**([*range*]) · Source, Examples

See *continuous*.range. If *range* is specified, implicitly uses d3.interpolateRound as the interpolator.

# *diverging*.**copy**() · Source, Examples

See *continuous*.copy.

# *diverging*.**unknown**() · Source, Examples

See *continuous*.unknown.

# d3.**scaleDivergingLog**([[*domain*, ]*range*]) · Source, Examples

A diverging scale with a logarithmic transform, analogous to a log scale.

# d3.**scaleDivergingPow**([[*domain*, ]*range*]) · Source, Examples

A diverging scale with an exponential transform, analogous to a power scale.

# d3.**scaleDivergingSqrt**([[*domain*, ]*range*]) · Source, Examples

A diverging scale with a square-root transform, analogous to a d3.scaleSqrt.

# d3.**scaleDivergingSymlog**([[*domain*, ]*range*]) · Source, Examples

A diverging scale with a symmetric logarithmic transform, analogous to a symlog scale.

### Quantize Scales

Quantize scales are similar to linear scales, except they use a discrete rather than continuous range. The continuous input domain is divided into uniform segments based on the number of values in (*i.e.*, the cardinality of) the output range. Each range value *y* can be expressed as a quantized linear function of the domain value *x*: *y* = *m round(x)* + *b*. See this choropleth for an example.

# d3.**scaleQuantize**([[*domain*, ]*range*]) · Source, Examples

Constructs a new quantize scale with the specified *domain* and *range*. If either *domain* or *range* is not specified, each defaults to [0, 1]. Thus, the default quantize scale is equivalent to the Math.round function.

# *quantize*(*value*) · Source, Examples

Given a *value* in the input domain, returns the corresponding value in the output range. For example, to apply a color encoding:

```
var color = d3.scaleQuantize()
.domain([0, 1])
.range(["brown", "steelblue"]);
color(0.49); // "brown"
color(0.51); // "steelblue"
```

Or dividing the domain into three equally-sized parts with different range values to compute an appropriate stroke width:

```
var width = d3.scaleQuantize()
.domain([10, 100])
.range([1, 2, 4]);
width(20); // 1
width(50); // 2
width(80); // 4
```

# *quantize*.**invertExtent**(*value*) · Source, Examples

Returns the extent of values in the domain [*x0*, *x1*] for the corresponding *value* in the range: the inverse of *quantize*. This method is useful for interaction, say to determine the value in the domain that corresponds to the pixel location under the mouse.

```
var width = d3.scaleQuantize()
.domain([10, 100])
.range([1, 2, 4]);
width.invertExtent(2); // [40, 70]
```

# *quantize*.**domain**([*domain*]) · Source, Examples

If *domain* is specified, sets the scale’s domain to the specified two-element array of numbers. If the elements in the given array are not numbers, they will be coerced to numbers. The numbers must be in ascending order or the behavior of the scale is undefined. If *domain* is not specified, returns the scale’s current domain.

# *quantize*.**range**([*range*]) · Source, Examples

If *range* is specified, sets the scale’s range to the specified array of values. The array may contain any number of discrete values. The elements in the given array need not be numbers; any value or type will work. If *range* is not specified, returns the scale’s current range.

# *quantize*.**ticks**([*count*]) · Source, Examples

Equivalent to *continuous*.ticks.

# *quantize*.**tickFormat**([*count*[, *specifier*]]) · Source, Examples

Equivalent to *continuous*.tickFormat.

# *quantize*.**nice**() · Source, Examples

Equivalent to *continuous*.nice.

# *quantize*.**thresholds**() · Source, Examples

Returns the array of computed thresholds within the domain.

# *quantize*.**copy**() · Source, Examples

Returns an exact copy of this scale. Changes to this scale will not affect the returned scale, and vice versa.

### Quantile Scales

Quantile scales map a sampled input domain to a discrete range. The domain is considered continuous and thus the scale will accept any reasonable input value; however, the domain is specified as a discrete set of sample values. The number of values in (the cardinality of) the output range determines the number of quantiles that will be computed from the domain. To compute the quantiles, the domain is sorted, and treated as a population of discrete values; see d3-array’s quantile. See this quantile choropleth for an example.

# d3.**scaleQuantile**([[*domain*, ]*range*]) · Source, Examples

Constructs a new quantile scale with the specified *domain* and *range*. If either *domain* or *range* is not specified, each defaults to the empty array. The quantile scale is invalid until both a domain and range are specified.

# *quantile*(*value*) · Source, Examples

Given a *value* in the input domain, returns the corresponding value in the output range.

# *quantile*.**invertExtent**(*value*) · Source, Examples

Returns the extent of values in the domain [*x0*, *x1*] for the corresponding *value* in the range: the inverse of *quantile*. This method is useful for interaction, say to determine the value in the domain that corresponds to the pixel location under the mouse.

<a name="quantile_domain" href="#quanti