Managing External References - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 675

a t t a C h M e n t a n d o v e r l a y : W h a t ' s t h e d I F F e r e n C e ? (Continued)
floor furniture plan. While the architectural team advances their design, a
member of the electrical design team could reference their individual draw-
ings to begin work on the first floor lighting plan. External references also
provide a way for project teams to assemble different plan sheets.
Because xrefs are such an integral part to so many projects, it's especially
important to think before you reference. Choosing the wrong reference type
can have an ill effect on the entire project.
In this image, the SQUARE.DWG has t wo drawings referenced into
it: PENTAGON.DWG and CIRCLE.DWG . The External Reference Type
for PENTAGON.DWG is Attachment, whereas the External Reference Type for
the CIRCLE.DWG is Overlay. Despite the differing reference types, there is
no difference in what's shown in the SQUARE.DWG ; you're able to see the
pentagon, circle, and square.
The difference between the Attachment and Overlay reference types is
not seen until you try referencing the SQUARE.DWG into another draw-
ing— TRIANGLE.DWG in our example. Take note of the objects displayed
in the TRIANGLE.DWG . Both the pentagon and square are shown; how-
ever, the circle is not.
the overlay reference type
When an xref reference type is set to Overlay, that reference is dropped
when referenced into another drawing. In the example, the CIRCLE.DWG
was referenced into SQUARE.DWG as an overlay reference. As a result, it
displays in SQUARE.DWG , but not when SQUARE.DWG is referenced into
another drawing ( TRIANGLE.DWG ).
(Continued)