Layer Maps
Layer Maps enables the pixels of another layer to control various aspects of the particles in the grid. Note that any layer used as a map must be pre-composed or pre-rendered to be used as a source for Form. In general, best results are obtained if the size of the layer map equals the size of the particle grid as defined in the Base Form controls.
Note: LAYER MAPS ARE DISABLED WHEN THE BASE FORM SPHERE IS SET. FORM DOES NOT CURRENTLY SUPPORT LAYER MAP INPUTS FOR SPHERE SHAPES.
There are five separate categories where you can specify an input layer map, including Color and Alpha, Displacement, Size, Fractal Strength, and Disperse.
Under each category, you can specify a source reference from an existing layer in your After Effects project. If you specify a source layer that contains no animation, Form will generate a static grid. If the source layer changes from frame to frame, Form will use this information to generate an animated grid. You can choose whether to apply a layer to a single plane (XY, XZ, or YZ) or to the XY plane while applying any animation to the Z plane.

All Layer Maps have a Map Over setting, which can be set to the following:
Off - the default, which indicates that the layer map is unused.
This diagram shows the mapping for each plane
XY - maps the current frame from the source Layer onto the XY plane on the particle grid

Original Source | Mapped over XY Plane with 300 x 300 particles

XZ - maps the current frame from the source Layer onto the XZ plane on the particle grid

Original Source | Mapped over XZ Plane with 300 x 300 particles

YZ - maps the current frame from the source Layer onto the YZ plane on the particle grid

Original Source | Mapped over XY Plane with 300 x 300 particles

XY, time=Z - maps the pre-composed layer image onto the XY plane of the particle grid. Any animation in the source layer is animated over Z so that Time Span spans the full grid in Z (see advanced example 2 below).
XY, time=Z+time is the same as the above, but also adds the current time to the mapping so that the end result is an animation (see advanced example 2 below).
Note: To get the right result for mapping, make sure that the Map Over plane has the appropriate particles to render an image. For example, if you are mapping over the XZ plane, make sure to have a grid of particles specified for this plane by settings the Particles in X and Particle in Z to values of 30 or more in each control.
Color and Alpha
Allows a source layer in After Effects to be used as the color and alpha channels for the particle grid. Choices include mapping RGB to RGB, which simply maps the color values to the particle colors; RGBA to RGBA, which maps color to the particle color and the alpha channel to the particle opacity across the grid; A to A (alpha to alpha), which maps just the alpha channel of the source layer to the opacity of each particle in the grid; and finally, luminosity to A, which maps the luminosity (the brightness of individual pixels) to the opacity values of the particles. Luminosity is useful for input layers that are have transparency information stored as an RGB image.

Color and Alpha Examples

Here is an example. In a real application, you'd probably use a denser particle grid, but here we will keep it sparse so you can see what is going on.
Particle grid without map:
Map:
Result when RGBA is mapped over XY:
Notice how the colors are used for each particle in the grid from the RGB channels, and the alpha channel defines transparency. This makes the grid particles 100% transparent where the alpha channel in the logo graphic is black.

Advanced Example 2
Another, more advanced application of the Color and Alpha map is to sculpt a particle shape in 3D using the Map Over "XY, time = Z" mode. Here is our animated map that we use as a Color and Alpha map:
Then we use a 50x50x50 particle grid (where each value corresponds to the Particles in X, Y, Z), we set the clip above to Map Over as Color and Alpha, and set Time Span to 8 seconds (the duration of the clip). What we get is a 3D sculpted static form:
By instead using the"XY, time = Z + time" mode, we get an animated 3D sculpture:
Displacement
This section allows you to displace particles in the form using the luminance values of another layer. A neutral gray (128, 128, 128 in 8-bit RGB) means no displacement. Colors that are darker than neutral gray will generate negative displacement (i.e., they will be pushed farther away from the viewer on the Z axis) and lighter colors result in positive displacement (i.e., they will be pushed closer to the viewer). The Displacement control also features a Functionality pop-up that lets you choose between mapping RGB channels to XYZ channels, or letting you specify the Layer source for each axis with separate source layer reference pop-ups, using the Layer for X, Layer for Y, and Layer for Z controls.
Size
This section lets you change the size of the particles in the form by using the luminance values of a layer map. Black regions of an image will have a particle size of zero, which will create holes in the form. White regions will have their particle size set to the maximum value that is set in the Particle section.
Fractal Strength

This section allows you to specify a layer whose luminance values define the extent to which any fractal information is used to perturb the form. Areas that are light in color (luminance) will be affected by the setting in the Fractal section, while darker parts will be less affected. Black parts will not be perturbed at all.

Example 3
Here is an example of a Fractal Strength layer in action:
We use the same Color and Alpha map as above:
Add some Fractal displacement with high settings for Displacement and the Octave Multiplier and Scale set to 2.0:
We set up a different comp in After Effects with a feathered mask moving from right to left:
We select this comp as source for the Fractal Strength layer map, and here is the end result:
Disperse
In a similar way to Fractal Strength, Disperse uses a layer map to modulate particle dispersion in the form. Here is what it looks like if we use the above example as a dispersion map instead:
The maximum amount of dispersion is set in Disperse & Twist controls.