If your book is a picture book or other fixed-layout book, you must indicate pre-paginated in the <meta property="rendition:layout"> tag in the <metadata> element within the OPF file. (See Defining Book Layout Metadata for instructions.) The pre-paginated option determines how the sample is generated. Without this option, the sample is generated as if the content is a text-heavy book like a novel. With this option, the sample is generated based on a percentage of the number of pages rather than word count. Apple Books determines the first page of the book (each page of a fixed-layout Book, whether a single page or a two-page spread, must be a separate XHTML file) and then generates the sample from a percentage of total page count. The sample looks to the landmarks <nav> block of the .opf to determine the start of the content of the book. For optimal samples, include epub:type="bodymatter" to indicate the beginning of the book's content. Note that a landmarks nav is required for fixed-layout books only if you do not provide a custom sample.