Flex Your Pages
What if the screen size changes? Say you want to view the same book on your phone that you started reading on your laptop. Or the screen itself doesn’t change size, but you decide that the text would be easier to read if the font size were larger. Both of those situations require some kind of flexible layout that can adapt to the changed sizes or shapes.
That’s where digital book design is headed now. (Not to mention magazines, newspapers, and websites.) It’s been called adaptive or flexible or responsive layout, and those who like that sort of thing get into intense arguments about what each of these terms means. But the point is to design pages that will still look good when one of the size factors changes.
Unfortunately, we don’t yet have tools that are finely tuned for this degree of adaptation. Just as designers have been forced to make a choice in web design for years already, would-be e-book typographers must select whether they want flexibility or precision. Page-layout applications like InDesign and QuarkXPress give us the tools to craft a carefully composed page, and those tools can automate a good deal of that process, if they’re used knowledgeably. 
For extended or immersive reading, where we’re reading a text that pulls us in, the length of the line becomes one of the most important design factors in how comfortable the text is to read. If the line is too long and the letters too small, it’s harder to read. There are other factors, too, like the amount of space between the lines, the space between the words, the tightness or looseness of letter-spacing, and the typeface used. They all interact.
The typographer’s job is to manipulate those variables to make a page that’s both inviting and readable. Of course, if we’re really motivated to read the text, we’re willing to put up with almost anything; when we’re bored with it, though, or find it difficult, that’s when the text needs all the help a typographer can give it.
Web design and other born-digital design has an unfortunate heritage of trying to cram as much information as possible onto one screen. The original reason for this was to avoid loading a new page from a web server, CD-ROM drive, or other medium. In the old days of slow computers and slow Internet connections, you might have to wait an annoyingly long period before a new page would appear on your screen.
But that limitation is largely gone today: not only do web pages load faster, but scripting can allow most of a web page to remain static while replacing just components of the page. Often having more pages with less text on each one works much better for reading than a single, long, overcrowded one. The typographer can design each page for readable text without consideration for days long past.
A book of straight prose is the simplest to lay out, since it consists of continuous text with maybe a chapter title or a subhead now and then. The most complicated books to design, whether in print or for the screen, are textbooks, cookbooks, and art books, all of which usually have a variety of elements on each page that need to be coordinated visually and functionally. That’s hard enough to do on a static page; it gets much harder when you’re trying to design for a page that might change its size and shape, or the size of its text, so that not everything will still fit on the same page.
That’s when you get into a complex set of algorithms, a system of “If this, then that, and therefore the other,” to determine how text should be laid out, where illustrations and sidebars and notes should go, and whether some images or page elements need to be moved to another page altogether. All of this is done to serve the reader, to make reading the book a smooth, easy process where the reader never has to think about any of this design stuff, or even consciously notice it.
Without that complex system of flexible layout, and competent designers to use it, many e-books have very awkward, hard-to-read page layouts. We’ve seen them all too often.