Download the visual PageSequence Catalog. Here is one page from the catalog. More-complete examples are to be found in a gallery here.
Also see PageSequence_ReadMe.txt, in the IDImposer Docs folder, for further details.
What are these PageSequence files?
A PageSequence file defines the order of imposition used in preparing books or booklets for folding and binding. You select a Page Sequence as one of the “Imposition Types” in the main IDImposer dialog. You will probably find it helpful to use the PageSequence Catalog or the gallery to help you choose the layout that best fits your job requirements for paper size and final printed page dimensions.
Books are typically produced in sections of 4 or more pages each. These sections are folded together, and bound with glue or sewing along the folded edges. A section is sometimes called a signature. Most signatures have a page count that is a power of 2, since they are typically created by folding a press sheet in half multiple times.
A signature, then, is a sheet of paper printed with four or more pages and folded one or more times to the approximate size of one page and in a manner which puts the pages in proper numbered order. The more common signature impositions are 4, 8, 16, 32, 64, and 128 pages, which are formed by folding the sheet in half one or more times. Less common are 12, 20, 24, and 36 page signatures, which require more complicated folding patterns.
It is common to use page sequence patterns that produce 2 or 4 signatures per sheet, to save impressions and better utilize the available area on the press sheet.
The PageSequences folder contains a number of the most common sheet layout definitions. But it is quite straightforward to copy one of the supplied PageSequence files and edit it to produce others.
In the PageSequence form definitions, the Page slots are numbered from 1, to be consistent with tradition and InDesign’s default Page naming.
These PageSequence files are by no means a complete collection of all of the folded imposition layouts (forms) that are currently in use. But I made the format easy to understand and use, so that you could make your own PageSequence files, too. The files are stored in the same RESOURCES folder that also contains this ReadMe.