Linear referencing, also called linear reference system or linear referencing system (LRS), is a method of spatial referencing over linear or curvilinear elements, such as roads or rivers. In LRS, the locations of physical features are described parametrically in terms of a single curvilinear coordinate, typically the distance traveled from a fixed point, such as a milestone. It is an alternative to referencing by geographic coordinates, which would involve two coordinates, latitude and longitude.
Point features (e.g. a signpost) are located by a single distance value while linear features (e.g. a no-passing zone) are delimited by two distance values, corresponding to beginning and end. If the subjacent linear referencing element or route is changed, only the linear coordinates of those locations on the changed segment need to be updated. Linear referencing is suitable for management of data related to linear features like roads, railways, oil and gas transmission pipelines, power and data transmission lines, and rivers. It is used in engineering, construction, and utilities management.