Berlin is Germany's capital and largest city, with over 3.5 million people in around 344 square miles. Its public-transportation network is expansive and efficient, but can be tricky to navigate.

This article is more than 6 years old. The Android and iOS app is called Jelbi ("yell-bee"), a catchy play on the German slang word for the color yellow, BVG's signature hue. However, Berliners could ...