iBooks Author: orientation
Each iBooks Author template is optimized for viewing on iPad in either landscape (horizontal) or portrait (vertical) orientation. When you create a book, you choose either a landscape or a portrait template.
If a book uses a landscape template: When a reader rotates iPad to portrait orientation, the book reformats slightly. For example, a graphic might appear to the side of text, rather than below it. Or, you can prevent the book from switching to portrait orientation by selecting “Disable portrait orientation” in the Document inspector.
As you create your book, you can use the Orientation buttons to see what the completed book will look like on iPad in each orientation. (The Orientation buttons do not change a template from landscape to portrait.)
If a book uses a portrait template: Even when a reader rotates iPad to landscape orientation, the book stays in portrait orientation. You can’t use the Orientation buttons with a portrait template.