MicroStation V8i contains several new features related to "Geo-Coordination", or the ability to specify the position of the contents of your design on the earth's surface. Once that position is established, the design can be easily coordinated with other data for which the geographic location is known.
MicroStation users almost always work in either two- or three-dimensional Cartesian coordinate systems. For designs that represent manufactured components or assemblies, there is no fixed earth location to consider, and Geo-Coordination does not apply. For designs of infrastructure that occupy a volume of less than about a cubic kilometer (buildings and industrial plants, for example) there is no need to consider the curvature of the earth as a factor, and designers prefer to work in a local coordinate system that is convenient for the building or plant. But as we shall see, establishing the geographic location of the infrastructure provides substantial advantages.
For larger-scale designs such as roadways, utility outside plant, and natural resource modeling, the conventional approach is to use a Cartesian approximation to the earth's surface that gives acceptable results in the vicinity of the design contents. In the United States, most roadway designs use State Plane coordinate systems. Other country and local governing bodies establish Geographic Coordinate Systems appropriate for their locations. Some natural resource companies and military organization also develop Geographic Coordinate Systems for their particular purposes. Most of the time, a MicroStation user can simply work in the Cartesian coordinate system without considering that it is actually a carefully chosen Geographic Coordinate System.
For a more in-depth discussion of Geographic Coordinate Systems and how they are chosen, see Geographic Coordinate Systems Fundamentals
MicroStation takes advantage of a knowledge of the geographic location of your design to provide additional capabilities.
Link updated. Thanks for pointing that out.
dead link: communities.bentley.com/.../geographic-coordinate-systems-fundamentals.aspx