The objective is to develop a model that defines the objects necessary for describing locations and the relationships between these objects. Objects include real-world and theoretical "anchors" of Mn/DOT's standard location reference systems (e.g., geodetic monuments, Public Land Survey corners, routes, mileposts, stations), geometric and topological representations of the transportation network (e.g., digitized line strings, topological links, nodes), and typical abstract or aggregated views of the network (e.g., pavement management segments, snow plow routes). [Mn/DOT 1993b]
Individual end users of systems which reference spatial locations each have their own "external" view of how to locate objects. Roadway inventory may use route/reference point, construction surveying may use alignment station/offset, cartographers may use coordinates, traffic forecasting may use link/node, and traffic accident reporting street addresses.
At the other end of the spectrum, different automated systems may each use different "internal" representation schemes for storing information in the computer. A CAD system, like Mn/DOT's Intergraph system represents roads as vectors on a drawing layer. ARC/Info approximates them as arcs (actually chords) on a map coverage. ORACLE Highways represents roads as rows in relational tables. An object based graphic data system like ODS models roads as individual objects with data and behavior consistent with a particular end user's view of the road.
The objective of this project is to develop a single, comprehensive, conceptual model of location information. This model fits between the various external and internal views (see Figure 1). As such, it must support all of the identified external views. The internal views can be thought of as individual vendors' interpretation of that part ( or all) of the conceptual model necessary to support their delivered functionality, internally represented in the manner which best supports, in their opinion, that functionality.