Understanding letterforms
As mapmakers, we may be tempted to simply jump in and choose a font that looks right for our map, but an understanding of some key elements of letterforms can help define why a particular font works with the rest of our map elements or not. While there are many components to letterforms, for our purposes, we only need to concentrate on a few, shown in the following figure:
Picture a sheet of notebook paper. The light blue lines printed on it correspond to the BASE LINE and the CAP LINE in the preceding figure. Ascender and Descender often extend over and under these lines, which can sometimes conflict with other map features (if too extensive), and can impact legibility in blocks of text. The X-height is the height of the body of a lowercase letter, which, in part, helps determine the visual weight of a font. If the x-height and the cap line are fairly close together, the font will appear heavier and more compact than if they are farther apart.
Leading, tracking, and kerning help determine the amount of white space in a label or paragraph. Leading refers to the space between base lines, which, in manual typesetting, was created by placing a thin strip of lead between the rows of type blocks. In ArcGIS Pro, leading is set using the Line spacing options under Text Symbol in the Format Text:
Kerning and tracking refer to the spaces between individual letters, but each has a specific function. Tracking allows you to spread letters out (which is helpful for labeling area features), or to compress them slightly to fit into tight spaces, and is controlled using the Letter spacing settings. Too much expansion or compression can impair readability, so this setting should be changed with care.
Kerning adjusts the spacing between letters to nest them slightly, so that gaps between narrower letters don't appear larger than those between wide ones, as shown in, Figure 4.2. Kerning is turned on by default in ArcGIS Pro, but if you want to disable it for some reason, just turn off the checkbox. Be aware that turning off kerning may not be an obvious difference in some fonts, but can greatly impact legibility in areas of dense labeling.
One last factor that impacts the way labels look on the map is the choice between serif and sans-serif. Serifs are the little flourishes that stick out at the edges of letters, and can impact visual weight, mood, and legibility and play a key role in the development of map grammar, detailed later in this chapter. Serifs can come in a variety of styles, which can increase or decrease the visual weight and change the flavor of the map, as shown in the following figure:
A general rule for lettering on maps is to never go smaller than 6 point type, but the size of the type may not appear to be consistent between fonts. Font size is based on points, which refer to the size of the block on which movable type was set. A one inch block holds 72 point font, but because of block positioning (accommodating ascenders and descenders) and the comparative roundness of letters, not all fonts appear the same at the same size, as seen in the following figure:
