Join Jeff Bartels for an in-depth discussion in this video Choosing whether to attach or overlay, part of AutoCAD 2009: Mastering References.
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When creating an external reference, we have a choice between Attach and Overlay. In this lesson we are going to learn the difference between these two options. Let me mention that this drawing that I have opened is a blank AutoCAD drawing. It contains no geometry and no layers; well, except for layer 0. I would like to start by externally referencing an AutoCAD drawing. Now, my Reference Manager is currently anchored on the side of my screen. Let me hover over this guy and we'll open him up. To reference my drawing I'm going to click the Attach DWG icon. We are going to navigate into the Chapter 3 folder, inside our exercise files directory, and I want you to come down and select drawing number 4, the prop drawing, and we'll click Open.
Whenever we create an external reference or an xref for short, we have the choice between Attachment and Overlay. Now, these settings only come into play if someone was to reference my current drawing. What these settings essentially do is control what happens to my reference drawing if someone references my current file. If I reference a drawing via Attachment and someone later x-references my current drawing, they will also get the file that I have referenced. If I reference a drawing via Overlay and someone later x-references my current drawing, they will not get the drawing that I have referenced. So these settings control what happens to my referenced file if someone references my drawing.
I am going to leave this set to Overlay, which is the default. I'm going to leave my boxes unchecked, and I'm going to come down and click OK. Now that my drawing has been referenced, I'm going to do a Zoom Extents so we can see it on screen. Let me pan this over just a little bit, and then let's take a look at our Reference Manager. Notice that even though I referenced only one drawing, I have got four drawings in this list. That's because the one drawing that I referenced, referenced three other drawings via Attach. If I click this slider and pull over, we can see this in the Type column. In fact, we can see it even better if we click the Tree view. Notice this is the drawing that I referenced and these three drawings are coming along for the ride. These files are also considered nested x-references, because they are a reference within a reference.
So knowing what we know now if I was to select the file that I have referenced and come down and change its type to Attach, if anybody references my current drawing, they are also going to get this one and these three. Now, sometimes nested xrefs can get out of control. That's why AutoCAD defaults to the Overlay method. That way if you reference drawings and someone references you, they are only going to get your drawing. I am going to set my Reference Manager back the way it was. Let's click the List view. I'm going to pan this over, and I'm going to change my Reference method back to Overlay. This way if someone references my file, they won't be getting all of my references.
When attaching xrefs remember that the attachment method you choose will control what happens to those references if someone references your drawing. If you are unsure of which method to use, the safest choice is to go with Overlay.
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