existing nodes and ways. Examples include turn restrictions on roads, routes that span several existing ways (for instance, a long-distance motorway), and areas with holes. Tags are key-value pairs (both arbitrary strings). They are used to store metadata about the map objects (such as their type, their name and their physical properties). Tags are not freestanding, but are always attached to an object: to a node, a way or a relation. A recommended ontology of map features (the meaning of tags) is maintained on a wiki. New tagging schemes can always be proposed by a popular vote of a written proposal in OpenStreetMap wiki, however, there is no requirement to follow this process. There are over 89 million different kinds of tags in use as of June 2017. The OpenStreetMap data primitives are stored and processed in different formats. The main copy of the OpenStreetMap data is stored in OpenStreetMap's main database. The main database is a PostgreSQL database, which has one table for each data primitive, with individual objects stored as rows. All edits happen in this database, and all other formats are created from it. Data from GeoNames is used for the search in OpenStreetMap. For data transfer, several database dumps are created, which are available for download. The complete dump is called planet.osm. These dumps exist in two formats, one using XML and one using the Protocol Buffer Binary Format (PBF). Data collection Map data is collected from scratch by volunteers performing systematic ground surveys using tools such as a handheld GPS unit, a notebook, digital camera, or a voice recorder. The data is then entered into the OpenStreetMap database using a number of software tools including JOSM and Merkaator. Mapathon competition events are also held by OpenStreetMap team and by non-profit organisations and local governments to map a particular area. The availability of aerial photography and other data from commercial and government sources has added important sources of data for manual editing and automated imports. Special processes are in place to handle automated imports and avoid legal and technical problems. OpenStreetMap data has been favourably compared with proprietary datasources, although data quality varied across the world. Software Editing of maps can be done using the default web browser editor called iD, an HTML5 application using D3.js and written by Mapbox, which was originally financed by the Knight Foundation. JOSM, Potlatch, and Merkaartor are more powerful desktop