Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Linear Referencing

OVERVIEW

Managers of artifacts with long linear structures (e.g., highways, pipelines, railroads) are generally unconcerned with the precise two-dimensional geographic coordinates of the entity they deal with. A locomotive is pretty well locked onto the railroad’s one-dimensional linear structure—unlike, say, an airplane, which can operate in three dimensions. As a result, many of the coordinate systems that have grown up around linear structures are different from those we have been talking about up to now. Terms like road miles, river miles, and rail miles are in common use in those industries. The average citizen who uses the Interstate Highway System will probably be familiar with the small green signs with numbers on them that indicate the number of miles from some origin—frequently a state border.

We are in the habit of representing linear structures with lines drawn between junction points (e.g., nodes). (Of course, these structures are portrayed on a two-dimensional field, but the smallest part of each such line is one-dimensional [a vector], so we call them one-dimensional, or linear.) The difficulty with simply representing such a structure—let’s take a highway, for example—from intersection to intersection is related to attributes. The requirement, so far in your studies, is that any GIS feature (whether point, line, or polygon), must be homogeneous in all its attributes. For example, all of a given cadastral polygon is owned by one entity, the taxes ...