City Sizes

Created on October 07, 2026

2026   ·   openstreetmap   maps   quiz   ·   code

I have always wondered what it would look like to overlay city outlines on a map. So today I built City Sizes, which loads city boundaries from OpenStreetMap and draws the outlines to scale with Leaflet on a greyscale map. You pick a reference city, and the others are placed next to it. The code is on GitHub.

What is the largest Swiss city that fits entirely within Frankfurt?

How many copies of Bern fit inside Rome?

And which four cities are these?

Zurich in red and four unlabeled city outlines overlaid to scale on a map of the Zurich region
Four secret cities overlaid on Zurich (about 90 km²). Hint: I will be moving to one of them in the coming months. #bigcitylife. Map data © OpenStreetMap contributors.

You can check your answers and build your own quiz on the live page. For the solutions, click on the Swiss candidates around Frankfurt and move them inside, count the Bern copies inside Rome, or the view the names of the four secret cities.

Note: most of the page’s features do not work on mobile phones.