editing applications that are better suited for advanced users. Vespucci is the primary full-featured editor for Android; it has been regularly released since 2009. StreetComplete is an Android app launched in 2016, which allows users without any OpenStreetMap knowledge to answer simple questions for existing data in OpenStreetMap, and thus contribute data. Maps.me and OsmAnd, two offline mobile map applications available for Android and iOS, both include limited OpenStreetMap data editors. Go Map!! is an iOS app that lets users create and edit information in OpenStreetMap. Pushpin is another iOS app that lets users add POI on the go. Surveys and personal knowledge Ground surveys are performed by a mapper, on foot, bicycle, or in a car, motorcycle, or boat. Map data was typically recorded on a GPS unit. In late 2006 Yahoo! made their aerial imagery available for tracing to OpenStreetMap contributors, which simplified mapping of readily visible and identifiable features. The project still makes use of GPS traces from volunteers which are used to delineate the more difficult to identify and classify features such as footpath, as well as providing ground-truth for aerial imagery alignment. Once the data has been collected, it is entered into the database by uploading it onto the project's website together with appropriate attribute data. As collecting and uploading data may be separated from editing objects, contribution to the project is possible without using a GPS unit. Some committed contributors adopt the task of mapping whole towns and cities, or organising mapping parties to gather the support of others to complete a map area. A large number of less active users contribute corrections and small additions to the map. Street-level image data In addition to several different sets of satellite image backgrounds available to OpenStreetMap editors, data from several street-level image platforms are available as map data photo overlays: Bing Streetside 360° image tracks, and the open and crowdsourced Mapillary and KartaView platforms, generally smartphone and other windshield-mounted camera images. Additionally, a Mapillary traffic sign data layer can be enabled; it is the product of user-submitted images. Government data Some government agencies have released official data on appropriate licences. This includes the United States, where works of the federal government are placed under public domain. Globally, OpenStreetMap initially used the Prototype Global Shoreline from NOAA. Due to it being oversimplified and crude, it has been mainly replaced by other government sources or manual tracing.