Humanistic
Humanistic typefaces are based on the proportion of Roman inscriptional letters. Considered the easiest san serifs to read, Humanistic type faces have easily apparent contrast in strokes and are more closely related to serif typefaces. A common example of a Humanistic typeface is Gill Sans.
Transitional
Also more closely related to serif typefaces, Transitional type has a more upright axis and a uniform stroke. A popular example of this kind of typeface is Helvetica.
Geometric
Geometric typefaces are (obviously) based on geometric forms. Some letter forms, like the lowercase ‘o’, form perfect shapes. Futura is a common typeface that is an example of Geometric typefaces.
