Washington DC's transit agency WMATA is preparing to publish a frequent network map, and wants your comments. To start, they're taking the approach of showing frequency as a highlight on the main network map, as this makes it easier to show how multiple overlaid routes combine to form a frequent line.
For over a decade now as a consultant I've been emphasising the need for transit maps to provide clear visual signals about frequency. I laid out the case on the blog here.
I have one comment: WMATA is defining "frequent" as every 15 minutes all day, but on the draft map their legend refers to "buses/hour," which is implicitly an average rather than worst case frequency. Nobody cares about average freqeuncy! Frequency maps are about a guaranteed worst case, so they should show only corridors where the longest scheduled gap between trips is 15 minutes. Four buses an hour may not guarantee 15 minute service if they're not scheduled with exactly even spacing. In fact, you can meet a standard of "four buses an hour" with four buses that all arrive in a bunch at the top of the hour, but in reality, that's a 60 minute frequency, not 15!