Lettering and typography have a long cartographic history. The guidelines for the use of text on a GIS computer display are no different from those developed for paper maps. Choices of type style, form, size, color, and placement are key in the design of a legible and organized display. Text in visualization applications can be treated as another symbol, one imbued with meaning through language and not through graphical abstraction. As such, choices of size and color should be made according to the guidelines of these visual variables outlined elsewhere in this unit.
Style. Popularly referred to as "font," text style is the geometric design of the letters themselves. Elements of text style include serifs ("finish" strokes like the little horizontal base of the lowercase L), line thickness, relative dimension ratios, and decorative ornaments. A GIS is often capable of producing dozens of fonts, but be aware that overuse of this capability leads to a confusing display. Generally, the fewer the type styles on the display the better. That said, there are some general conventions often used by cartographers. Since style differences are much like hue differences in that they are best at distinguishing nominal differences, one common convention is to use serifed fonts for natural features like rivers, mountain ranges, and islands, and "sans serif" (without serif) fonts for human-built features like cities and political units. Good type style choices for displays are easy to read and do not detract or distract from the overall message of the display. In other words, the viewer should notice the data and not the unusual font of the text.
Form. A type style can take many forms, like "bold," "italic," "light," or "upright." There are few cartographic conventions dealing with form, since the choices are far more limited than those of style. One form convention worth noting, however, is the frequent italic form of labels of water features. Almost universally, rivers, lake, oceans, bays, and other water features are labeled using italics, perhaps to represent flow and fluidity.
Size. Be very careful with size. GIS displays have the ability to scale type to any size, from 0.5 point (very small, unreadable, less than 1 mm in height) all the way to 180 point (2 inches tall, the size of a banner headline) or more. Cartographers often overestimate humans' ability to see very small text and our ability to notice small differences in size of text. As a general rule, do not use text smaller than 8 points in a display. In addition, do not use more than three sizes of the same type style and form on the same map, and use size variations of over 25%. That is, use a "small" size of, say, 10 points, a "medium" of 12.5, and a "large" of 16.
Placement. As discussed elsewhere, GIS displays have a significant advantage over paper maps in that symbolization and design choices can be altered very easily and quickly. This is an important consideration in placing text on the display. As the data displayed changes, text can be moved to accommodate new data while ensuring legibility of the text. There are some general rules, however, that should be observed at all stages of GIS display design. This is a partial list from Robinson (p. 416):
• names should be entirely on land or on water.
• lettering should be oriented to match the orientation structure of the map. On a large-scale map, this means that type should be parallel with the upper and lower edges of the map; in small-scale maps, type should be parallel to the parallels.
• type should not be curved unless it is necessary to do so
• disoriented lettering (that is, not parallel to the map edge or the lines of latitude) should never be set in a straight line but should always have a slight curve.
• names should be letterspaced as little as possible. That is, there should not be wide spaces between the letters in the name. Exceptions to this guideline involve labeling large area features like mountain chains or oceans.
For a detailed list of placement do's and don'ts, see Imhof.