MeridianWay is a web app that finds two walking routes between two addresses for a chosen date and time: one with as much sun as possible, and one with as much shade as possible. A time slider shows how both routes change from sunrise to sunset.

Since around 2020, I’ve wanted a Google Maps-style option to choose between a route in the sun and one in the shade, alongside “fastest” and “shortest”. On my third attempt last July, I finally got the whole thing working.¹

For each segment, the app estimates when the walker will reach it, calculates the sun’s position at that moment, and checks whether nearby buildings or trees block the sun. During a 45-minute walk, the sun’s azimuth changes by roughly 11°, which can be enough to move the shaded side of a street.

MeridianWay displaying a sunny route in Lausanne

In Switzerland, the app uses building footprints and heights from swissBUILDINGS3D 3.0 (beta), a dataset from swisstopo². I converted the dataset for the whole country and serve it from Cloudflare R2 through a small bounding-box service. On one test route in Lausanne, 26% of buildings had a mapped height in OpenStreetMap³, compared with 100% in swissBUILDINGS3D 3.0. Outside Switzerland, the app uses OSM building heights where they are available in the vector basemap tiles, and default values for the rest. Trees and forests also come from OSM, with seasonal leaf cover.

Routes are computed using OpenRouteService, developed by the HeiGIT, the Heidelberg Institute for Geoinformation Technology. The basemap comes from Stadia Maps, OpenMapTiles and OpenStreetMap. Terrain shadows are not modelled and roofs are treated as flat, so the results are estimates, not a guarantee that every part of a route will be shaded.

MeridianWay is a free, non-commercial side project with no account and no ads. It is available in French, German, Italian and English, with an initial version in Romansh. The code is open-source under the MIT licence.

Footnotes

1. Transparency note: I built and maintain MeridianWay as a non-commercial side project. I have no affiliation with swisstopo or any of the other data providers mentioned.↩︎

2. The Federal Office of Topography of Switzerland.↩︎

3. OpenStreetMap or OSM is a collaborative, open-licensed map of the world.↩︎