Linear Referencing and Dynamic Segmentation

Dynamic segmentation is a computer-based database management system using the principles of relational algebra and topological integrity to minimize error and maximize efficiency of map analysis and display. Linear features are stored as nodes and arcs and provide only the minimum of geometric properties for proper display on maps.

When these linear features, such as roads and railways, have multiple attribute tables, dynamic segmentation is used to query and display such attributes. Examples include the number of accidents at different parts of the pavement or speed limits that differ within the same segment. Since geometric nodes and arcs are the foundation of linear features stored in a geographic information system (GIS), dynamic segmentation becomes quite useful to represent attribute data that do not sync perfectly with the geometric range of the linear features.

Utilities and transportation networks often have information without geographic coordinates. Usually, this information is based on a fixed reference point along a route. The data stored are referred to as a linear referencing system. For example, highway accidents often are coded based on the nearest intersection and the network distance from the intersection (i.e., the driving distance from the accident location to the nearest intersection). Tables containing such information are known as milepost tables. Using a map, one can dynamically calculate the coordinate information and display accident sites. Since dynamic calculations can be done using computer memory, the storage of such information permanently is deemed redundant. In addition, since highway maps and other linear maps are stored and updated independently of the accident tables, there is no need to separately change the accident coordinates whenever a highway map is updated (since, in the milepost table, there are no accident coordinates to begin with). This approach restricts the propagation of error and is important since geometric coordinate error cannot be eliminated. Another benefit is that line segments need not be broken into smaller pieces. Actual breaks are limited to intersections with other lines or change of direction in the line segment.