Managing External References - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 690

That's all there is to adding images to AutoCAD drawings. You can move and
rotate the image using the same tools as with any other object. You can resize
the image by selecting the frame and adjusting the grips. You get access to some
rudimentary image-editing tools when you double-click the image frame. Feel
free to experiment with those tools, but do not be concerned about altering the
image file; these adjustments affect only the image's display inside AutoCAD.
Putting Xrefs to use
External references have many different uses. I'll describe two common applica-
tions to illustrate their range.
Suppose you're working on a project as an interior designer and a subcontrac-
tor to the lead architect. The architect gives you a drawing of a floor plan that
is still undergoing changes. You load this file onto your hard drive in a specially
designated folder, and then you externally reference it into your drawing as a
background—a drawing to be used as a reference to draw over. You can proceed
to lay out furniture, partitions, and so on while the architect is still refining the
floor plan.
At an agreed-on time, the architect gives you a revised version of the floor plan.
You overwrite the one that you have on your computer with the latest version. You
can then reload the xref into your furniture layout drawing, and the newer ver-
sion of the floor plan will be the background. In this example, the lead architect
might also send the same version of the floor plan to the structural and mechani-
cal engineers and the landscape architect, all of whom are working on the project
and using the architect's floor plan as an xref in their respective host drawings (see
Figure 13.32).
Xrefs are often used when parts of a job are being done in an office where a
network is in place. Suppose a project involves work on several buildings that
are all on the same site. If the project uses xrefs, each building can be externally
referenced to the site plan. This keeps the site plan drawing file from getting too
large and allows the project work to be divided among different workstations;
in addition, the project manager can open the host site plan and keep track of
progress on the whole project (see Figure 13.33).
These two applications for setting up xrefs in relation to a host file are appli-
cable to almost any profession or trade using AutoCAD.