Not much use for route planning: this map was really made just to show how the routes that ran into the city centre were grouped into geographic regions and denoted by a colour and an icon. While stops along the transit mall are now marked with boring old letters, back then these cheery and oh-so-1970s symbols guided you to the bus stop you needed. Also very 1970s: the tightly-kerned Avant Garde typeface.
Source: TriMet’s “How We Roll” blog – article since removed
Curios to what zone the bus lines colored with black ink refer?
Looks like crosstown routes to me (i.e., they don’t go downtown/to the Mall), Matthew.