The city’s Transportation Department has hit an app that tracks New Yorkers’ block-by-block walking routes with a cease-and-desist letter. DOT directed the app to stop using WalkNYC branding, disable the website and app, and remove physical and online material promoting it. App users are directed to a form indicating Puccio wants to share letters of support with DOT from app users. A screenshot of the WalkNYC app shows a message about the cease and desist letter. The app WalkNYC, which became available on the App Store in May, logs each city block that users walk by marking routes with green on a digital map.