Clipping paths and vector paths serve the same purposeidentifying what will be visible or invisiblebut they do so at two different levels. Clipping paths are used with images destined for page layout programs, delineating areas of visibility for the image as a whole. Vector masks are used in a similar manner to show and hide areas of individual layers within an image.
Open, closed, and compound paths can all be used to create both clipping paths and vector masks. You must name a work path to save it before you can convert it to a clipping path. Double-clicking a work path in the Paths palette and renaming it saves it, and you can then use the Paths palette menu command Clipping Path.
The Clipping Path dialog box includes a Flatness field. Never enter a value for flatness unless your imagesetter is having trouble outputting curves. The field overrides the device's native setting for vector reproduction.
You can create a vector mask for a layer in either of two ways. You can first create the path and then assign it as a vector mask, or you can create the vector mask and then define it with a path. With or without an active path, use the menu command Layer, Add Vector Mask. Alternatively, you can -Option-click (Mac users) or Ctrl+Alt-click (Windows users) the Add Layer Mask button at the bottom of the Layers palette.