Public transit & GTFS

A transit feed is a timetable stored as a database. Routes are labels, trips are journeys, and the times live in one enormous table that only makes sense once a calendar has said which dates each trip runs on. Every question here — how often, how far, how many people — is a join across four or five files, and the calendar is the one most often skipped.

What makes the subject hard is time. A GTFS time can read 25:10:00, a holiday can remove one timetable and add another, and the travel time between two places depends on the minute you leave, because missing a bus by a minute costs its whole headway. Almost every error in this topic is a number that looks reasonable: a frequency counted across both directions, a catchment drawn as a circle, a travel time taken from the best departure of the hour.

The concepts below cover the feed, its calendar, headways and accessibility; the how-to guides read, clip, map and route across a real feed; and the fixes are filed under the symptom — times past midnight, empty dates, straight-line routes and travel times that flatter the network.

Learning paths run through this topic too — see the end of this page.