The City of Detroit has issued a challenge to the OpenStreetMap US community to make Metro Detroit the best openly mapped region in the world. This session will provide an overview of data sources and methodologies used in this challenge, highlighting Detroit’s initiatives to make city data available to everyone. We will showcase a series of lightning talks presenting the outcomes of the challenge, with a focus on efforts that combine the wealth of available data and technology with local knowledge and experience. We will discuss what we learn that can be sustained for ongoing mapping in Detroit and applied to similar initiatives in other cities