The community agrees on certain key and value combinations for the most commonly used tags, which act as informal standards. OpenStreetMap's free tagging system allows the map to include an unlimited number of attributes describing each feature.
Each tag describes a geographic attribute of the feature being shown by that specific node, way or relation. OpenStreetMap represents physical features on the ground (e.g., roads or buildings) using tags attached to its basic data structures (its nodes, ways, and relations).
