Building map grammar

When we develop a system of font styles, we are essentially building the grammar of the map. The combination of labels and symbols helps our audience learn new features by comparing them to the structures used for familiar features. 

The first piece of this is the map hierarchy. When we assign fonts by feature class, size, or importance, we are helping our map reader quickly determine which parts of the map should be viewed first. Large, bold fonts leap forward and demand attention, while smaller and lighter fonts recede, providing information when needed, but not assertively.

We can also use fonts as variables. The contrast between serif and sans-serif lends itself to qualitative distinctions. Any time we change fonts, even if they are both serif or sans-serif, we are clueing our reader into a change in information. Color, form, and width can also indicate qualitative changes, but be careful they don't move to a different place in the hierarchy by appearing heavier or lighter.

Quantitative changes are perhaps easier to indicate through size and weight, and also the use of uppercase. Color can sometimes indicate quantitative change, if using lighter and darker values of a single hue, for example. 

The determination of what is important on a map can merely be a factor of size, but may also be linked to the purpose of the map. A city central to the topic may be represented in a heavier font than a larger city appearing on the map. Remember that the point of map grammar is to lead your user through the information in a coherent way.

Regardless of which features carry more weight and why, it is absolutely important to not overpower the map with labels, and that legibility is not impaired.