If you plan on visiting Washington DC check out the applications that are available. Many of them are done by government organizations like the National Park Service application for the area around the National Mall. Moving around the district check out the Metro system application that provides information about both buses and Metro train. The Smithsonian app for the National Zoo is quite useful even though it didn’t seem that the GPS work quite well enough when I was there. And for Arlington National Cemetery there’s a wonderful app that’ll help you find a particular grave or point you in the right direction to visit many points of interest in the cemetery.