Type is measured in a variety of ways, including points or pixels. Web based-type has limitations on size. The differences in screen resolutions, platforms, and browser rendering capabilities mean that there's a lot of variation in the way type is displayed on a screen. So while size always matters, Web designers have their work especially cut out for them when they try to use markup to work with type. The proportions of any given typeface compared to another are important.
Proportional relationships help indicate what role each typeface plays on a page.
The direction in which your typeface runs significantly impacts the way the type is perceived. Type direction is referred to as orientation. Horizontal type is more stable, involving little or no movement. That's why it's used as body text. When designing for impact, however, you should think about pursuing other orientation options.