linearreference

Linear reference, or linear referencing, is a method for specifying locations along linear features such as roads, rivers, or pipelines using a measure along the feature rather than Cartesian coordinates. A network of linear elements, called alignments or routes, is assigned a continuous measure scale from a defined starting point. A position on the network is described by an alignment identifier and a measure along that alignment, for example Route 52 at 12.5 kilometers.

Key concepts include alignments, routes or links, measures, and events or assets located along the network. In geographic information systems, linear referencing is implemented through a linear referencing system (LRS). The measure value (often called M) can be in units such as meters or miles. Dynamic segmentation supports creating sub-segments along an alignment without altering the underlying geometry.

Common operations include locating a point by measure, determining the measure of a given point, converting a Cartesian coordinate to a measure along the nearest alignment, and splitting or merging alignments at specified measures. These capabilities enable precise, measure-based indexing along networks.

Applications span transportation planning and operations, asset management for roads and utilities, traffic incident reporting, maintenance scheduling, and environmental monitoring along a corridor. Linear referencing allows events, assets, and observations to be referenced consistently even as network geometry is updated.

Advantages include robustness to small geometric shifts and the ability to integrate events along a continuous network. Effective use requires consistent topology, clearly defined start points and units, and appropriate data models to support measure-based queries and operations.