Jarrett Walker at Human Transit makes the case for bus system maps that clearly indicate route frequency, and uses King County Metro as an example of how not to do that. It’s an argument I made in May, but treated with Jarrett’s usual eloquence and depth. As usual, go read the whole thing.
If a street map for a city drew every road with the same kind of line and label, so that Interstate 5 looked no different from the smallest gravel cul-de-sac, we’d say it was a bad map. But it’s not wrong, the mapmaker would say! No, it’s not, but it’s misleading. If we can’t identify the major streets, we can’t see the basic shape of the city, and without that, we can’t really make use of the map’s information.
The only thing I’d add comes from a conversation I had after I wrote that piece. Given the politics of city/suburb relations, a 15-minute frequency map is explosive simply because it illustrates how much better service is in the city. After all, only 11 of 35 high-frequency segments even leave the city, and none but Link on Sundays. That’s for good reason, but it’s also not what a lot of people want to see.