With Books 3.0, in-book links provide a fundamentally important step in the evolution of internet-connected books the reader can research like Wikipedia entries, dictionary entries, author-provided notes and websites, Google maps and other sites without ever leaving the book.
Books 3.0 in-book research makes it easy through the use of ‘marginalia’ – symbols along the side of the book that can be turned on and off at will. See an example here.
In-book map links provide a fun way to get a feel for the setting of a particular scene in the story. See an example here.
These are fully searchable google maps that can extended the reading experience.