THIS ARTICLE IS IN DEVELOPMENT
== Introduction ==
Most agencies likely publish a system or network map of their bus service. A system map can be helpful in familiarizing the customer with area coverage, but can also paint a misleading picture of actual availability. Many agencies have routes which only operate at certain times of day, such as peak period or overnight, which might appear on the system map alongside routes which run all day. A "frequent network map" includes only routes which run on a consistent and high frequency, visualizing both actual connections and the highest level of mobility on the system.
== Layers of Service ==
A standard system map can be misleading when it includes every route on the system
. Some routes may only operate during peak periods, nighttime, or weekends, for example. Including these routes alongside those that run a regular frequency all day misleadingly represents coverage that might not exist or imply route connections that are impossible to make.
The "frequent network" is made up only of bus routes which run regularly throughout the entire service day. Walker also defines this network as routes running every 15 minutes or more frequently<ref>Walker, Jarrett. Human Transit (blog) "The Case for Frequency Mapping" http://www.humantransit.org/2010/08/basics-the-case-for-frequency-mapping.html. 6 August 2010</ref>. However, even small agencies with twenty, thirty, or sixty-minute headways system-wide can take advantage of the principle of differentiating maps by "all day service" and others. Even small agencies can have routes which operate only at specific times or on specific days, such as a Wednesday "Shopper Shuttle". Including these services on the map might be well-intentioned, but will mislead customers to assume it runs like the rest of the system.
Notes alongside the map can help, but customers will miss notes. The route could be differentiated with a different style of line, or excluded from the system map.
In 2012, King County metro released a new system map which does include all services (including light rail alongside bus and ferry routes), but differentiates routes between frequent, peak period only, and all-day infrequent. The "rapid" routes stand out in bold, eye-catching red lines. The all-day frequent routes are in strong black lines and numbers, while peak-only service is in a faded blue. The visual distinction makes the difference between service level and geographic coverage very clear and understandable for the customer.