The first consideration we have is the limitation of SPACE we have to work within. The aspect ratio of a screen, the size of a page be it for a book , magazine, newspaper, the size of a billboard, the shape of a business card are all governed by geometry & scale.
Once we know our space constraint we can begin to design information to fit it artistically. So this time we work in reverse we know the form and so we design for functionality of information transfer.
Here are some examples of size contraints for the visual display of information