Each map is based on the situation at the end of the year in question. Transit services are shown only if they were frequent (running at least every 20 minutes during the mid-day off-peak period on weekdays), included sections with stops at least every 1.5 to 3 km, and were grade-separated or had absolute priority (i.e. crossing gates or equivalent) at all road crossings. Through-running into streets or other surface rights-of-way where the transit vehicles did not have absolute priority at intersections is shown with thinner lines. (Streetcars and other services with no grade-separated or crossing-gated sections, intercity/regional services with wide stop spacing throughout their runs, and very short lines less than 250m long, are not shown.)