# Line system (typography)

In typography , the (optical) upper and lower edges of the visible glyphs of the different upper and lower case letters form a system of lines .

A four-line system - also known as the four-line scheme or main line system - is obtained when lowercase letters ( minuscules ) are used. The upper two lines are formed from the upper edges of lowercase letters with ( k, h, b etc.) and without ascender ( x, o, a etc.), their common lower edge - the baseline - forms the third line and the lower edge the lower case letter with descender ( q, p, g etc.) forms the fourth. The height of the capital letters - the i. d. It is usually a little smaller than with lowercase letters with ascender - is ignored here.

A three-line system (or three-line scheme ) results from a small caps font (the lower case letters are shown as small capital letter variants). The three lines here correspond to the top three lines of the four-line system - although the middle one is sometimes slightly higher.

A two-line system (or two-line scheme ) results when only capital letters ( capitals ) are used, the upper and lower edges of which form the lines.

## Four-line system

Typographic horizontal guides and heights

### The main lines

The letters stand on the baseline (or baseline ). The center line, or x-line, is the upper limit of lowercase letters such as o , u , n, or x . The k line is the upper limit of lowercase letters that protrude upward beyond the center line, such as b , d , f, and k . The p-line is the lower bound of lowercase letters that cross the baseline down, like g , p , q, and y .

### Height sections of the lowercase letters

The center length or x-height is the distance between the baseline and the center line. Lowercase letters such as a , e , n or z have only one middle length, which in principle can be further subdivided into e , s , k and x and sometimes a , g and w . The ascender refers to those parts of the lower case letters that exceed the center line upwards, as in b , d , f and k . Notwithstanding this, DIN 16507-2 measures the ascender from the baseline. The descender denotes those parts of the lower case letters that cross the base line downwards, as seen at g , p , q and y . The lowercase letter j has both ascenders and descenders.

### Further height dimensions

As cap height refers to the height of the capital letters ( uppercase ). The upper length of the lowercase letters usually protrudes slightly above the height of the capital letters, in order to use this optical trick to make straight and curved letters appear equally high. In other words, the H-Line is often a little lower than the K-Line. The accent height is the vertical distance of the top vertex of accented capital letters (e.g. Ê) from the baseline.

The typeface height is the largest vertical extension of a typeface. It is usually given as hp height , i.e. the sum of the upper, middle and lower length. If necessary, the uppercase height and descender or the accent height and descender are added. In lead type, the cone height is the height of the lead letters with which the characters were printed. Since the letters are slightly higher than the letters, the height of the cone is slightly larger than the height of the typeface.