Europe

As Europe reels from extreme heatwaves, a German app is helping people stay cool by mapping shaded walking routes. The app uses sun and shadow data to guide commuters away from heat-exposed streets.

Here is more information about the app (archived) including links to the source code, API, and such.

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Europe is witnessing a summer of unprecedented climate realities ... facing an urgent question: How do we live, move, and survive in cities that are actively overheating?

The answer may lie in a German digital tool developed by the non-profit organisation Heidelberg Institute for Geoinformation Technology (HeiGIT). Designed to transform daily commutes, the app calculates the coolest, most shaded path through a city, allowing citizens to avoid direct sun exposure.

What started as a region-specific research project is now evolving into a large-scale blueprint for climate-adapted mobility. The app currently offers its routing service in more than 80 major German cities and continues to expand.

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The Algorithm That Steers People Away From Heat

When the sun shines intensely, open spaces can quickly turn into heat traps. Pedestrians often cross to the shaded side of the street or take a longer route through a park to avoid direct sunlight. The app mimics this behaviour by using high-resolution shadow data to guide people through shaded passages and away from sun-exposed roads.

Julian Psotta, Product Owner for Technical Innovation at HeiGIT, says, "What started as a research question in Heidelberg has now grown into an operational heat-avoiding routing application. We are looking forward to fine-tuning it to the individual needs of different cities and building climate-adapted mobility based on their data."

Through heat-avoiding routing, the app helps municipalities understand their heat risks and respond to them in a targeted manner. But what has created the need for such a tool?

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How The App Finds The Coolest Route

The app launched its first version in Heidelberg in the summer of 2024. Today, the routing engine runs on openrouteservice (HeiGIT's open-source routing platform) and uses OpenStreetMap data as its underlying road network. A custom Solar Index helps the algorithm avoid hot, sun-baked roads and instead choose shady, tree-lined routes.

Because the sun's position changes constantly, the app is dynamic as well. It offers pedestrians different routes depending on the time of day. For example, a commuter walking from Worms' main train station to the Rhine promenade will receive different route suggestions depending on when they open the app:

• In the morning: The app suggests taking Wilhelm-Leuschner Street, then walking along Martinsgasse and Judengasse to maximise morning shade.
• In the afternoon: As the sun shifts, the coolest route changes entirely, directing pedestrians through Goethe Street.
• The regular route: The slightly shorter, traditional route via Siegfried Street and Berliner Ring is actively bypassed by the algorithm because of its high sun exposure.

The creators say the aim is to make the consequences of urban heat on daily life visible and measurable.

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From Germany To The World

Now that the application covers all 16 federal states in Germany, the team hopes to expand globally. However, taking a climate tool worldwide requires building trust with local partners first.

Lisa Shkredova, Public Relations Manager at HeiGIT, explains, "Whenever we expand into a new area, it is very important to have local partners who can validate the data. That's why we started small and only later expanded to multiple cities across Germany."

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Archived