When is it OK to use landscape page orientation?
Research papers and manuscripts are generally composed in portrait rather than landscape orientation—that is, vertically rather than horizontally. This is the default setting for most word-processing systems, and most academic print or PDF publications are longer than they are wide. Occasionally, however, a figure included in a work that is otherwise oriented vertically needs to be oriented horizontally for readability.
The MLA’s report on 2016 enrollments in languages other than English, for example, includes several graphs that show data from nearly six decades. As you can see in figures 1a and 2, the data points and labels along the x-axis would be too compressed to display legibly if the graphs were oriented vertically, and it would be difficult for readers to make sense of the data (Looney and Lusin 24, 26).
Switching the orientation of pages in a work can be . . . disorienting. It’s best to avoid alternating between vertical and horizontal orientation when possible and, when not, to group horizontally oriented figures together, to minimize the disruption for readers.
Looney, Dennis, and Natalia Lusin. Enrollments in Languages Other Than English in United States Institutions of Higher Education, Summer 2016 and Fall 2016: Final Report. Modern Language Association, June 2019, www.mla.org/Enrollment-Report.