Roads, also called arterials, are fussy features (see Figure 6.1 for color suggestions).
They can include everything from the major interstate highway to the dirt road
behind your house. A map showing all the road types from dirt to autobahn with the
same color and line width, at any scale, would simply look ridiculous unless your
goal was to produce a jumble of lines (see inset, this section). There are exceptions
to every rule but for the most part our roads must be separated into size classes and
symbolized accordingly.