An xref, short for external reference, is one drawing file linked into another. Instead of copying a site survey or a structural grid into every sheet, you reference it, so when the referenced file changes, every drawing that uses it shows the change the next time it is opened. Xrefs are how most AutoCAD offices keep a set consistent, and they explain a few surprises you see later in the PDFs.
What an xref is, in one minute
- The host drawing is the file you work in, for example a floor plan sheet.
- The xref is a separate DWG shown inside it, for example the base plan, the survey or a consultant's layout.
- The xref's geometry is not stored in the host. The host stores the path to the file and draws it each time.
- You cannot edit the xref's lines from the host directly; you open the referenced file or edit it in place with the reference editing tools.
Attach or overlay?
| Attach | Overlay | |
|---|---|---|
| Nested references | Carried along: if your file is referenced elsewhere, its xrefs come too | Not carried along: only visible in the file where you overlaid it |
| Typical use | Parts that belong to the drawing, such as a title block or a base plan | Context you only need to see, such as another discipline's layout |
Paths: the source of most xref problems
The host remembers where the xref lives. If the folder moves or the set is sent to someone else, the reference can break and the drawing shows "not found" instead of the geometry.
- Relative paths survive moving the whole project folder; use them when the set travels.
- Full paths break as soon as the drive letter or folder changes.
- Before sending DWGs outside the office, use eTransmit or bind the xrefs so the receiver gets everything.
Binding an xref
Binding turns the reference into part of the host drawing. Use it for an issue or archive copy, when the drawing must stand alone. Binding is a one-way step: later changes to the original file no longer reach the bound copy.
What happens to xrefs when you export to PDF
A PDF does not keep references. When you plot or export a sheet, everything visible, including every xref, becomes part of the PDF's linework. A few things are worth knowing:
- Clipped xrefs (xclip) export only the visible part. If something is missing in the PDF, check the clip boundary first.
- Layers: if you export PDF layers, xref layers keep their combined names, such as
BASE|A-WALL, so the receiver can still switch disciplines on and off. - File size: a detailed survey or a dense consultant xref is often what makes a sheet's PDF heavy. Freeze layers you do not need before plotting.
- Unloaded or missing xrefs do not print at all, so a broken path can silently drop part of a sheet. Check the External References palette before you issue.
Reviewing the PDFs
Once the set is exported, the person reviewing it usually works on the PDF, not the DWG. Heavy xref-laden sheets are exactly where general PDF viewers slow down. Ncored, the PDF editor we built in our architecture studio, opens drawing sets of 50 MB and more fast on Windows and Mac, lets you measure to scale and compares two revisions of a sheet, so a changed xref shows up as a highlighted change.
Frequently asked questions
What does xref mean in AutoCAD?
External reference: another drawing file displayed inside the current one, linked rather than copied.
What is the difference between attach and overlay?
An attached xref travels with your drawing when your drawing is referenced elsewhere; an overlay does not.
Why is my xref not showing?
Most often a broken path after the files moved, or the xref is unloaded. Open the External References palette, check the status and repath if needed.
Do xrefs appear in the PDF?
Yes, if they are loaded and visible when you plot. In the PDF they become ordinary linework, not links.
Related: exporting DWG to PDF for review, converting a PDF back to DWG in AutoCAD, PDFs with layers.
Further reading: free DWG viewers.