GEOMETRY OF TYPEFACE
edited by: Olivera Stojadinović
January 2005

translation into English: Danijela Tomazović
November 2009

The letter baseline is an imagined line on which the letters sit. More precisely, on the baseline sit the appropriate horizontal serifs.

The basic letter height or the height of the lowercase letters (x-height) is determined based on the lowercase x letter height. Lowercase letters without ascenders or descenders reach the baseline.

The height of lowercase ascenders (ascent) is the line reached by lowercase letters ascenders. The height of lowercase descenders (descent) is the line reached by lowercase letters descenders. These heights are measured starting from the baseline up, that is, down.

The height of capital letters (caps height) is smaller or equal with the height of lowercase ascenders.

In case the height of the ascenders is higher than the caps height, this is recognized as five-lined system. If these heights are aligned, the system is four-lined.

The lowercase and caps heights are determined by the position of horizontal serifs. The curved letters or the ones with slanted serifs depart from this line in a small value, equally on bottom and on top. This overshoot ensures for all the letters to optically seem as of the same size. The overshoot value is up to 4%, depending on the letter shape.

The lowercase letters height line sits on horizontal serifs of lowercase letters and horizontal strokes of “f” and “t” letters. This is how the lowercase letter “o” starts a bit below the baseline, and its top curve goes above the lowercase letter height line in equal part.

The letter size or height (M-square) is the distance between descent and ascent lines. Its value equals to the total of ascent and descent heights. By the rule, all the letters sit somewhere in between these two lines. However, capitals' diacritics can partially cross the letter height. Also, in some manuscripts with long strokes, it is allowed for them to end outside the letter height lines. This means that there is a possibility for the letters from consecutive lines to partially overlap, in case the lines are set without additional spaces, which sometimes is designer's intention.

It is common to add additional space in between when setting the lines, which in manual typeset was achieved by adding the slugs or strips of lead (leading ).

The larger ratio between x-height and M-square (x/M) is, the higher x-height is and ascenders and descenders are shorter so the letter is more readable in small sizes. The letters with longer ascenders and descenders are more elegant and are more easily read, but take more space, so are used in places where the aesthetic component is more important than cost optimization. The letters with short endings are used in publications that need the large amount of data to be placed on as smallest space as possible, while readability is preserved, which makes this kind of letters suitable for dictionaries and directories.