In the age of Google maps, it’s easy to assume we've got our cities covered. Yet many of the most important aspects of a city aren’t mapped: how easy is it to walk in this city? Is this a safe bike route? Is this area accessible to wheel chair users? These are just some of the important questions that crowdsourced mapping can help to answer.

For example, Wheelmap, an online map developed by the German NGO Sozialhelden, enables people to share information about how accessible places are by wheelchair. Launched in 2010, users have mapped 500,000 locations across the world.

The map has two functions: one is to let people know how accessible the city is, the other is to change the way city governments think about accessibility and give NGOs and activists a tool to use to lobby for improvements. Other examples include Clean Air Asia’s WALKability app, which people can use to score places based on how easy they are to walk around and Safecity, a platform for people to share their personal stories of sexual harassment in public spaces in India and Nepal.