Essential linear referencing system vocabulary
Below are terms that are encountered when working with linear referencing systems.
Dynamic segmentation is the process of computing the map locations of events stored and managed in an event table along route features and displaying them on a map. The term dynamic segmentation is derived from the concept that line features need not be split (in other words, "segmented") each time an attribute value changes—you can "dynamically" locate the segment.
Using dynamic segmentation, multiple sets of attributes can be associated with any portion of an existing linear feature independently of where it begins or ends. These attributes can be displayed, queried, edited, and analyzed without affecting the underlying linear feature's geometry.
An event is a linear, continuous, or point feature that occurs along a route feature. Anything that occurs on or describes a route feature can be an event. In the transportation field, examples of events might include pavement quality, accident sites, and speed limits. Events are stored in event tables.
Event tables contain information about assets, conditions, and events that can be located along route features. Each row in the table references an event, and its location is expressed as measurements along a route feature. There are two types of route event tables: point event tables and line event tables.
Linear referencing method
A linear referencing method (LRM) is a system of measure for linear features that are represented as an offset from a known location along the length of a given feature. LRMs can be offsets from milepost locations along a highway, a measured distance from a known starting point, or a distance and direction from an asset location. LRMs are usually represented as a unit of measurement, such as miles or kilometers, but they can also be unitless, such as address ranges or a proportion.
A measure that is added to a line feature. M-values are stored in the m-coordinate of each vertex on a route feature. M-values are used to measure the distance along a line feature.
A value stored along a linear feature that represents a location relative to the beginning of the feature, or some point along it, rather than as an x,y coordinate. Measures are stored as m-values on route vertices. Measures can be any unit of measurement, such as miles, meters, and time.
A route is any line feature, such as a street, highway, river, or pipe, that has a unique identifier and a system of measurement. Routes are stored in a route feature class.
Within Production Mapping, a line feature is only referred to as a route if it has a unique identifier and has measure values (m-values).
Route feature class
A route feature class is a collection of routes with a common system of measurement stored in a single feature class (for example, a set of all highways in a county). A route feature class differs from a standard line feature class in that, along with x- and y-coordinates, it also stores an m-coordinate (x,y,m).
Straight line diagram
A diagram of a linear referencing route feature where the route is depicted as a straight line instead of showing the geometry of the feature. Such diagrams include one straight line to represent the route and additional rows above or below the route to depict events or features along the road. Straight line diagrams are often used for highway or pipeline management.