Reflowable vs. fixed layouts

Publication file formats can be separated into two categories, reflowable formats and fixed layout formats (but the distinction is not always that simple).

Fixed layout formats are typically designed for printing, they include PostScript and Adobe PDF. A vast majority of PDF files have a fixed layout, but occasionally some PDFs can contain extensions to make them reflowable. The content of fixed layout files is displayed the same way things will appear once printed. Images, words, paragraphs, columns are positioned at fixed coordinates within a page. The size of the page is imposed.

Reflowable formats are typically designed to be displayed on a screens for which the size is not known or imposed. HTML and plain text are reflowable formats.

Figure 1: a typical page of text.

Figure 2: the same page of text using a fixed layout on a different screen size.
Only a fraction of the page can be displayed at a time.
The user has to scroll right and left to read each line of text.

Figure 3: the same page of text reflowed on a different screen size.
The width of a line of text always matches the width of the screen.
This is the best reading experience for this text and this screen size.

The format used for content on the Amazon Kindle is a reflowable file format. There is no way to create Kindle content with a fixed page layout. Specifically, the file format solves the following issues:

• Content is reflowed to optimally adapt to the screen size.
• The user (rather than the publisher) chooses the font family, font size, margin size, line spacing, etc. to make the reading more comfortable. All these parameters are highly dependent on the device and the user. It is therefore logical to adjust them at reading time.
• The file format and its compression guarantee a fixed time to display any given page of the book. In order to display page 1000 of a book, you do not need to decompress or repaginate the 999 previous pages. We consider it essential to have a very responsive reading applications.
• Images can be embedded in different sizes.