diff --git a/README.md b/README.md
index 5395202b4e..c8a3fcffd7 100644
--- a/README.md
+++ b/README.md
@@ -2936,7 +2936,7 @@ Constructs a Delaunay triangulation of the samples, and then for each pixel in t
 
 #### Plot.interpolatorRandomWalk({*random*, *minDistance* = 0.5, *maxSteps* = 2})
 
-For each pixel in the raster grid, initiates a random walk, stopping when either the walk is within a given distance (*minDistance*) of a sample or the maximum allowable number of steps (*maxSteps*) have been taken, and then assigning the current pixel the closest sample’s value. The random walk uses the “walk on spheres” algorithm in two dimensions described by [Sawhney and Crane](https://www.cs.cmu.edu/~kmcrane/Projects/MonteCarloGeometryProcessing/index.html), SIGGRAPH 2020.
+For each pixel in the raster grid, initiates a random walk, stopping when either the walk is within a given distance (*minDistance*) of a sample or the maximum allowable number of steps (*maxSteps*) have been taken, and then assigning the current pixel the closest sample’s value. The random walk uses the “walk on spheres” algorithm in two dimensions described by [Sawhney and Crane](https://www.cs.cmu.edu/~kmcrane/Projects/MonteCarloGeometryProcessing/index.html), SIGGRAPH 2020.
 
 ## Markers
 
diff --git a/src/marks/contour.d.ts b/src/marks/contour.d.ts
index 183fe42e9b..2b06111d24 100644
--- a/src/marks/contour.d.ts
+++ b/src/marks/contour.d.ts
@@ -4,15 +4,89 @@ import type {Data, RenderableMark} from "../mark.js";
 import type {Thresholds} from "../transforms/bin.js";
 import type {RasterOptions, RasterSampler} from "./raster.js";
 
-export interface ContourOptions extends Omit<RasterOptions, "imageRendering"> {
+/** Options for the contour mark. */
+export interface ContourOptions extends Omit<RasterOptions, "interval" | "imageRendering"> {
+  /**
+   * Whether to apply linear interpolation after marching squares when computing
+   * contour polygons; defaults to true. For smoother contours, see the **blur**
+   * option.
+   */
   smooth?: boolean;
+
+  /**
+   * The value can be specified as a channel based on the sample *data*, or as a
+   * function *f*(*x*, *y*) to be evaluated at each pixel if the *data* is not
+   * provided.
+   */
   value?: ChannelValue | RasterSampler;
+
+  /**
+   * How to subdivide the domain into discrete level sets; defaults to *auto*;
+   * one of:
+   *
+   * - a named threshold implementation such as *auto* (default) or *sturges*
+   * - a function that returns an array, count, or range interval
+   * - a range interval
+   * - an array of *n* threshold values for *n* - 1 bins
+   * - a count representing the desired number of bins (a hint; not guaranteed)
+   *
+   * For example, for about ten contours:
+   *
+   * ```js
+   * Plot.contour({fill: (x, y) => Math.sin(x) * Math.cos(y), thresholds: 10, x1: 0, x2: 1, y1: 0, y2: 1})
+   * ```
+   *
+   * See also the **interval** option.
+   */
   thresholds?: Thresholds;
+
+  /**
+   * How to subdivide the domain into discrete level sets; a stricter
+   * alternative to the **thresholds** option allowing the use of shorthand
+   * numeric intervals; one of:
+   *
+   * - an object that implements *floor*, *offset*, and *range* methods
+   * - a named time interval such as *day* (for date intervals)
+   * - a number (for number intervals), defining intervals at integer multiples of *n*
+   *
+   * For example to create an isoline every 10 meters on a topographic map:
+   *
+   * ```js
+   * Plot.contour(volcano.values, {interval: 10, width: volcano.width, height: volcano.height})
+   * ```
+   */
   interval?: RangeInterval;
 }
 
-export function contour(options?: ContourOptions): Contour;
-
+/**
+ * Returns a new contour mark, which creates contour polygons from spatial
+ * samples. If *data* is provided, it represents discrete samples in abstract
+ * coordinates **x** and **y**; the **value** channel specifies further abstract
+ * values (_e.g._, height in a topographic map) to be spatially interpolated to
+ * produce a raster grid of quantitative values (like in the raster mark), and
+ * lastly contours via marching squares, which are rendered as vector polygons.
+ * For example, to generate filled contours from a topographic map, where the
+ * color corresponds to the contour threshold value:
+ *
+ * ```js
+ * Plot.contour(volcano.values, {width: volcano.width, height: volcano.height, fill: Plot.identity})
+ * ```
+ *
+ * The **fill** and **fillOpacity** channels may alternatively be specified as
+ * functions *f*(*x*, *y*) to be evaluated at each pixel centroid of the
+ * underlying raster grid (without interpolation). For example, to draw a
+ * contour plot of a two-dimensional function:
+ *
+ * ```js
+ * Plot.contour({x1: -1, x2: 1, y1: -1, y2: 1, fill: (x, y) => Math.atan2(y, x)})
+ * ```
+ *
+ * With the exception of the **x**, **y**, and **value** channels, the contour
+ * mark’s channels are not evaluated on the initial *data* but rather on the
+ * generated contour multipolygons.
+ */
 export function contour(data?: Data, options?: ContourOptions): Contour;
+export function contour(options?: ContourOptions): Contour;
 
+/** The contour mark. */
 export class Contour extends RenderableMark {}
diff --git a/src/marks/raster.d.ts b/src/marks/raster.d.ts
index 33acb74911..fdf6fe9d0f 100644
--- a/src/marks/raster.d.ts
+++ b/src/marks/raster.d.ts
@@ -1,54 +1,254 @@
 import type {ChannelValueSpec} from "../channel.js";
 import type {Data, MarkOptions, RenderableMark} from "../mark.js";
 
+/**
+ * The built-in spatial interpolation methods; one of:
+ *
+ * - *nearest* - assign each pixel to the closest sample’s value (Voronoi diagram)
+ * - *barycentric* - apply barycentric interpolation over the Delaunay triangulation
+ * - *random-walk* - apply a random walk from each pixel, stopping when near a sample
+ */
 export type RasterInterpolateName = "nearest" | "barycentric" | "random-walk";
 
+/**
+ * A spatial interpolation implementation function that receives samples’
+ * positions and values and returns a flat array of *width*×*height* values.
+ * *x*[*index*[0]] represents the *x*-position of the first sample,
+ * *y*[*index*[0]] its *y*-position, and *value*[*index*[0]] its value (*e.g.*,
+ * the observed height for a topographic map).
+ */
 export type RasterInterpolateFunction = (
+  /** An array of numeric indexes into the channels *x*, *y*, *value*. */
   index: number[],
+  /** The width of the raster grid in pixels; a positive integer. */
   width: number,
+  /** The height of the raster grid in pixels; a positive integer. */
   height: number,
-  X: number[],
-  Y: number[],
-  V: any[]
+  /** An array of values representing the *x*-position of samples. */
+  x: number[],
+  /** An array of values representing the *y*-position of samples. */
+  y: number[],
+  /** An array of values representing the sample’s observed value. */
+  values: any[]
 ) => any[];
 
+/**
+ * A spatial interpolation method; either a named built-in interpolation method,
+ * or a custom interpolation function.
+ */
 export type RasterInterpolate = RasterInterpolateName | RasterInterpolateFunction;
 
+/**
+ * A source of pseudo-random numbers in [0, 1). The default source is seeded to
+ * ensure reproducibility.
+ */
 export type RandomSource = () => number;
 
-export type RasterSampler = (x: number, y: number, facet: number[] & {fx: any; fy: any}) => any;
+/**
+ * A sampler function, which returns a value for the given *x* and *y* values in
+ * the current *facet*.
+ */
+export type RasterSampler = (
+  /** The horizontal position. */
+  x: number,
+  /** The vertical position. */
+  y: number,
+  /** The current facet index, and corresponding *fx* and *fy* value. */
+  facet: number[] & {fx: any; fy: any}
+) => any;
 
+/** Options for the raster mark. */
 export interface RasterOptions extends Omit<MarkOptions, "fill" | "fillOpacity"> {
+  /** The horizontal position channel, typically bound to the *x* scale. */
   x?: ChannelValueSpec;
+  /** The vertical position channel, typically bound to the *y* scale. */
   y?: ChannelValueSpec;
+
+  /**
+   * The starting horizontal position (typically the left edge) of the raster
+   * domain; the lower bound of the *x* scale.
+   *
+   * If **width** is specified, defaults to 0; otherwise, if *data* is
+   * specified, defaults to the frame’s left coordinate in *x*. If *data* is not
+   * specified (as when **value** is a function of *x* and *y*), you must
+   * specify **x1** explicitly.
+   */
   x1?: number;
+
+  /**
+   * The ending horizontal position (typically the right edge) of the raster
+   * domain; the upper bound of the *x* scale.
+   *
+   * If **width** is specified, defaults to **width**; otherwise, if *data* is
+   * specified, defaults to the frame’s right coordinate in *x*. If *data* is
+   * not specified (as when **value** is a function of *x* and *y*), you must
+   * specify **x2** explicitly.
+   */
   x2?: number;
+
+  /**
+   * The starting vertical position (typically the bottom edge) of the raster
+   * domain; the lower bound of the *y* scale.
+   *
+   * If **height** is specified, defaults to 0; otherwise, if *data* is
+   * specified, defaults to the frame’s top coordinate in *y*. If *data* is not
+   * specified (as when **value** is a function of *x* and *y*), you must
+   * specify **y1** explicitly.
+   */
   y1?: number;
+
+  /**
+   * The ending vertical position (typically the bottom edge) of the raster
+   * domain; the lower bound of the *y* scale.
+   *
+   * If **height** is specified, defaults to **height**; otherwise, if *data* is
+   * specified, defaults to the frame’s bottom coordinate in *y*. If *data* is
+   * not specified (as when **value** is a function of *x* and *y*), you must
+   * specify **y2** explicitly.
+   */
   y2?: number;
+
+  /** The width (number of columns) of the raster grid, in actual pixels. */
   width?: number;
+
+  /** The height (number of rows) of the raster grid, in actual pixels. */
   height?: number;
+
+  /**
+   * The effective screen size of a raster pixel, used to determine the height
+   * and width of the raster from the frame’s dimensions; defaults to 1.
+   */
   pixelSize?: number;
+
+  /**
+   * A non-negative pixel radius for smoothing; defaults to 0. Note that
+   * blurring is applied on the values (before the color scale is applied) if
+   * quantitative, and after (on the materialized pixels), if ordinal.
+   */
   blur?: number;
+
+  /**
+   * The spatial interpolation method, when using *data* samples. One of:
+   *
+   * - *none* (or null, default) - assign each sample to the containing pixel
+   * - a named interpolation method, such as *nearest*, *barycentric*, or *random-walk*
+   * - a custom interpolation function
+   */
   interpolate?: RasterInterpolate | "none" | null;
+
+  /**
+   * The [image-rendering attribute][1]; defaults to *auto* (bilinear). The
+   * option may be set to *pixelated* to disable bilinear interpolation for a
+   * sharper image; however, note that this is not supported in WebKit.
+   *
+   * [1]: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/image-rendering
+   */
   imageRendering?: string;
+
+  /**
+   * The fill, typically bound to the *color* scale. Can be specified as a
+   * constant, a channel based on the sample *data*, or as a function *f*(*x*,
+   * *y*) to be evaluated at each pixel if the *data* is not provided.
+   */
   fill?: ChannelValueSpec | RasterSampler;
+
+  /**
+   * The opacity, typically bound to the *opacity* scale. Can be specified as a
+   * constant, a channel based on the sample *data*, or as a function *f*(*x*,
+   * *y*) to be evaluated at each pixel if the *data* is not provided.
+   */
   fillOpacity?: ChannelValueSpec | RasterSampler;
 }
 
-export function raster(options?: RasterOptions): Raster;
-
+/**
+ * Returns a raster mark which renders a raster image from spatial samples. If
+ * *data* is provided, it represents discrete samples in abstract coordinates
+ * **x** and **y**; the **fill** and **fillOpacity** channels specify further
+ * abstract values (_e.g._, height in a topographic map) to be spatially
+ * interpolated to produce an image.
+ *
+ * ```js
+ * Plot.raster(volcano.values, {width: volcano.width, height: volcano.height})
+ * ```
+ *
+ * The **fill** and **fillOpacity** channels may alternatively be specified as
+ * functions *f*(*x*, *y*) to be evaluated at each pixel centroid of the raster
+ * grid (without interpolation).
+ *
+ * ```js
+ * Plot.raster({x1: -1, x2: 1, y1: -1, y2: 1, fill: (x, y) => Math.atan2(y, x)})
+ * ```
+ *
+ * If **width** is specified, **x1** defaults to 0 and **x2** defaults to
+ * **width**; likewise, if **height** is specified, **y1** defaults to 0 and
+ * **y2** defaults to **height**. Otherwise, if *data* is specified, **x1**,
+ * **y1**, **x2**, and **y2** respectively default to the frame’s left, top,
+ * right, and bottom coordinates. Lastly, if *data* is not specified (as when
+ * **value** is a function of *x* and *y*), you must specify all of **x1**,
+ * **x2**, **y1**, and **y2** to define the raster domain.
+ */
 export function raster(data?: Data, options?: RasterOptions): Raster;
+export function raster(options?: RasterOptions): Raster;
 
+/**
+ * Applies a simple forward mapping of samples, binning them into pixels in the
+ * raster grid without any blending or interpolation. If multiple samples map to
+ * the same pixel, the last one wins; this can introduce bias if the points are
+ * not in random order, so use Plot.shuffle to randomize the input if needed.
+ */
 export const interpolateNone: RasterInterpolateFunction;
 
+/**
+ * Constructs a Delaunay triangulation of the samples, and then for each pixel
+ * in the raster grid, determines the triangle that covers the pixel’s centroid
+ * and interpolates the values associated with the triangle’s vertices using
+ * [barycentric coordinates][1]. If the interpolated values are ordinal or
+ * categorical (_i.e._, anything other than numbers or dates), then one of the
+ * three values will be picked randomly weighted by the barycentric coordinates;
+ * the given *random* number generator will be used, which defaults to a [linear
+ * congruential generator][2] with a fixed seed (for deterministic results).
+ *
+ * [1]: https://en.wikipedia.org/wiki/Barycentric_coordinate_system
+ * [2]: https://github.com/d3/d3-random/blob/main/README.md#randomLcg
+ */
 export function interpolatorBarycentric(options?: {random?: RandomSource}): RasterInterpolateFunction;
 
+/**
+ * Assigns each pixel in the raster grid the value of the closest sample;
+ * effectively a Voronoi diagram.
+ */
 export const interpolateNearest: RasterInterpolateFunction;
 
+/**
+ * For each pixel in the raster grid, initiates a random walk, stopping when
+ * either the walk is within a given distance (**minDistance**) of a sample or
+ * the maximum allowable number of steps (**maxSteps**) have been taken, and
+ * then assigning the current pixel the closest sample’s value. The random walk
+ * uses the “walk on spheres” algorithm in two dimensions described by [Sawhney
+ * and Crane][1], SIGGRAPH 2020.
+ *
+ * [1]: https://www.cs.cmu.edu/~kmcrane/Projects/MonteCarloGeometryProcessing/index.html
+ */
 export function interpolatorRandomWalk(options?: {
+  /**
+   * An optional source of pseudo-random numbers in [0, 1). Called at each step
+   * of the random walk algorithm with arguments *x*, *y*, and *step*. If not
+   * specified, defaults to a seeded random number generator.
+   */
   random?: RandomSource;
+
+  /**
+   * The random walk ends by “snapping” to the closest sample if closer than
+   * this distance (in pixels).
+   */
   minDistance?: number;
+
+  /**
+   * After this number of steps, which defaults to 3, lift the **minDistance**
+   * requirement and snap to the closest sample.
+   */
   maxSteps?: number;
 }): RasterInterpolateFunction;
 
+/** The raster mark. */
 export class Raster extends RenderableMark {}
diff --git a/src/transforms/bin.d.ts b/src/transforms/bin.d.ts
index eca387479d..2a4a182dcf 100644
--- a/src/transforms/bin.d.ts
+++ b/src/transforms/bin.d.ts
@@ -81,6 +81,8 @@ export interface BinOptions {
    * ```js
    * Plot.rectY(numbers, Plot.binX({y: "count"}, {thresholds: 10}))
    * ```
+   *
+   * See also the **interval** option.
    */
   thresholds?: Thresholds;