Numerous small and large variations in lines allow mapmakers to communicate all sorts of facts, stories, and concepts. A thin line may mark a minor road; an undulating line may track a river; and a straight line along the edges will often give the map itself a border. Although these lines now seem obvious, mapmakers developed these conventionalized, but still flexible, symbols slowly over time. By standardizing these symbols, texts that direct mapmakers how to use lines spread a European tradition of mapping throughout the world. The amazing variety in types of lines is most apparent in texts that explicitly teach mapmaking, a few of which you can see in these examples.