One advantage AutoCAD's software has over the traditional drafting table is the ability to insert the work of your colleagues into your current drawing as an xref, or external reference to a DWG file. AutoCAD enables your company's employees to collaborate by combining their drawings as attachments or as overlays. The difference between the two methods is subtle, but may have consequences for your employees' workflow, your company's computer resources and network performance.

Referencing Your Drawing

The difference between adding a xref drawing as an overlay or an attachment becomes evident when you or someone else uses the combined document later. Unlike overlaid xrefs, attached xrefs will include any xrefs they themselves contain as well. For instance, you may attach a colleague's floor plan to your current lighting drawing to complete your assignment. If other employees just need to use your lighting work as an xref, they will find the floor plan included as well. If you originally added the floor plan as an overlay, however, it would not bundled with your lighting drawing.

Circular References

The ability to nest xrefs can lead to a conundrum called circular reference. For example, you can insert a colleague's drawing that in turn also includes the drawing you are currently working on as an attached xref. Your drawing now needs her drawing, but her drawing tries to load your document as an xref. Circular referencing could have been avoided if your colleague had added your drawing as an overlay instead. Fortunately, the current version of AutoCAD can spot and break up circular references.

Computer Performance Considerations

The overlay method may be less resource intensive than loading xrefs as attachments. While your drawing may contain many other drawings with overlayed xrefs, no nested xrefs are brought along. On the other hand, if one or more of the drawings you need contain multiple, superfluous nested drawings, you may waste processor cycles, system RAM and dedicated graphics memory in the course of loading xrefs you don't need.

Network Consequences

Whether your current drawing uses nested or overlaid xrefs, it does not contain any actual DWG files. Instead, the drawing contains file links that help AutoCAD locate the xrefs wherever they are on the network or on your local workstation. Your company's network performance may suffer, however, if you have to load and insert drawings that reference multiple, attached drawings you don't actually need. Also, attached, nested xrefs may affect your employees workflow if any of the drawings they reference are missing, renamed or relocated.