| Target | Aligns/distributes relative to… |
|---|---|
| Composition | The composition frame. |
| Outside | The same as Composition, but layers land just outside the frame edges instead of flush against them. Handy for positioning layers off-screen before or after a slide in/out. |
| Selection | The combined bounding box of your current selection. |
| Key Layer | The first layer you selected (the key layer). Every other selected layer moves; the key layer never does. |
| Title Safe | After Effects’ title-safe margin, set in Preferences > Grids & Guides. Hold Alt/Option while clicking an align or distribute button to use the action-safe margin instead. |
Some Align to targets disable specific buttons or modifiers that wouldn’t make sense together. For example, Outside disables centering, since “outside” is only meaningful at an edge. See Modifiers.