Neglecting Accuracy

February 29th, 2024 | by Andreas Richter

(4 min read)

Humans are mapping the world for orientation. They try to put something three-dimensional on a small two-dimensional sheet of paper. We already had a short glimpse on how to map the world accurately. In addition to representing the world, maps in general also display possible ways of transport. Having a closer look at urban areas we know paper maps from the good old times and map applications in mobile devices from nowadays. Also, accurate aerial images are very helpful to get some orientation. But, while we are trying to improve accuracy of such maps, why are public transport maps often not spatially accurate and do not reproduce reality? They are boxy and do not resemble distances and locations in reality.

Finding your way out of the hell of public transport networks can get difficult. (Stockholm, image by Andreas Richter)

Mapping the world not always means to map it accurately. Next to geographical and navigation maps also topological maps exist out there:

  • Most common are road network maps. Nowadays they differ between standard definition (SD) maps, representing roads as network with nodes and edges (where edges can follow the course of the road) and high definition (HD) maps, which include also lane-level details such as their topography. Additionally, maps can contain information about transport links, points of interests and – in their HD version – road topography for micro-routing.

  • Road topography and beyond is part of cadastral maps. In general, they cover real estate information but they also model infrastructure assets. Both is used to manage road as well as rail topography by the corresponding operators.

  • Road network maps may already be used for navigation (routing). Dedicated navigation maps include additional technical information for localization (e.g., maritime navigation data telling about the light pattern of the light houses). For automated driving, localization data can also be about the environment and its scenery elements. Classification of these objects and their features can support the perception of automated driving systems.

  • Next to these kinds of maps there are also thematic maps. They are used to portray the geographic pattern of a theme in a geographic area. For example, they illustrate how agricultural crops are distributed through a country, or, where different types of industry are predominant. Socio-demographic data can be shown as well, such as population density, traffic demand, mobility accessibility and many more. To emphasize the differences of these themes between different countries, the size of a country is often scaled according to the topic, which makes the world look totally different.

Public transport is part of our daily mobility business and would fit quite well into the road and rail network maps. But for decades, public transport is mapped in a schematic way. The question is why, because it all started with geographically accurate representations of cities or countrysides while overlaying abstract individual lines of different public transport routes for easy identification.

At the end of the 19th century, positional accuracy began to be neglected in maps in favor of focusing on topology. One of the major drivers was the Brit Harry Beck. His famous work is the map of the London Underground. The idea was to increase readability and understandability by focusing only on the public transport itself. If stations are located close to each other, it is sometimes complicated to label all station names on the map in a readable way (especially, if you want to display different characters for different languages). Next, sometimes there is a lack of space for putting everything in the map. The transport vehicles have limited space to show the line or the whole network in their interior. The bus stop booths also have limited availability to put up big posters. The idea was to apply space-saving together with more clarity regarding the stations along the line. The solution was to schematize the maps, using only fixed angles such as 0, 45 and 90 degrees and straight lines. Sometimes, for iconic ring lines such as the Moscow metro ring, a circle was used.

Image: Real-world layout (left) converted into schematic representation (right).

Color grading was applied to distinguish between different lines and line style for different transport modes. Thickness of lines often resembles the headway of the public transport and sometimes the travel time between stations is added as well.

Also, the representation of stations was schematized especially for transit stations to better explain where you can switch from one line to another. The reason is that it is often unclear if different lines are using the same platforms, or, if different buildings are just connected by linkways. To add even more complexity, information about zone pricing was integrated, which added an additional level of complexity regarding schematic readability and efficient use of space. All of these design concepts lead to a public transport representation that is reflecting geographic reality only partly.

This very schematic representation was very popular for quite some time but now the trend goes back. Maybe this correlates with digital map applications getting used more commonly than before. They are showing the area in a topographical way because they often provide aerial images as well, fusing them with information from the topographical layer. Thus, on your mobile device, public transport lines follow the topographical flow. It gets complicated to translate this to schematic transport maps. To bring both closer together the schematic concepts get extended by adding a little bit of spatial accuracy such as distances of the stations and a more accurate course of the lines. The representation is still following a schematic representation with straight lines and fixed angles but some variations of curves are used to add some more reality. Also, structuring features of the city such as rivers, parks and lakes are able to be represented.

The Serbian Jug Cerović is one of the famous advocates for more realistic maps. He created guidelines for drawing good metro maps in eight simple movements.

Public transport map of Berlin 2023 by Berliner Verkehrsbetriebe (left) and berlintransitmap.de (right).

In the One World Metro book he explains some additional principles and schematics of creating public transport maps such as locating stations in a systematic way while still representing their real location or applying different bendings to lines to better meet reality while arranging stations in the flow of lines at the same time. A wonderful example is https://berlintransitmap.de, which compares a new public transport map with the current “robot-like” and many historic maps. The website explains the simplicity of the new style and why it might be better to understand. Check it out to make your own opinion about the need of spatial accuracy!

It seems that schematizing a plan can lead to overdoing it which can result in public transport maps getting too abstract. It is worth to bring back reality without neglecting abstraction. As always, it is worth to keep in mind more than only one goal.

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