Attaching References
OpenCities Map 's referencing tools let you view other models as you work on the active model, much the way overlays are used in the real world. With overlays, you work on the top overlay, while referring to the information on one or more overlays below.
You can reference models from the open DGN file, or from other DGN's that may or may not currently be opened by other users. Similarly, other users can reference the model that you are working on. Referencing is a powerful tool in a multi-discipline office; in particular, where many people are working on different aspects of the same project.
Note: When you attach a reference with working units set to US Survey Feet to a model whose working units are set to Feet (International Feet), or vice-versa, you get an alert window. The alert window says that the active model and the reference model have different working units, namely US Survey Feet and International Feet. Since the two units are nearly identical, mixing them can result in subtle problems, particularly for design projects that span more than a mile. If you are sure you want to attach this reference, click OK; otherwise, click Cancel. You can disable this alert window by setting the MS_REF_NOSURVEYFOOTCHECK configuration variable to 1.