Lost in paper space

Should paper space be your standard?

AutoCAD Release 11 marked the debut of two momentous features: xrefs and paper space. The xreference feature had precedents in manual pin-bar drafting and in competing CAD programs such as MicroStation, but paper space appeared as a magnificent new invention and remains unique to AutoCAD. As with so many AutoCAD features, there's hardly unanimity about when and how to use them.

Some offices embrace xrefs eagerly and employ them for plot sheet assembly and all manner of component re-use. Other offices, after being burned by undisciplined use of xrefs, avoid them altogether. Some offices employ paper space as standard operating procedure for all plot sheet drawings. Even in companies with users well-versed in both features, personal preferences and office customs lead to different ways of using paper space and xrefs.

You need to develop reasonable consistency in how you use these features within your company. Your office CAD standards should include guidelines about when and how to use them, especially for drawing setup (see "The well-rounded CAD standard"). The decision about when to use paper space is often complicated and contentious. The "when to use xrefs" question can be nearly as troublesome at first, but the answer is usually obvious once you answer the paper space question. Though paper space and xrefs work well together for creating some kinds of drawings, in many cases they offer competing methods for project drawing setup and organization.

Paper space quandary
The AutoCAD user community is full of strong paper space advocates, but it also includes strong detractors. I'll confess to being a moderate detractor—but not because I think paper space is a bad feature. It's an indispensable tool for some kinds of drawings and a useful tool for others. But many offices use it indiscriminately. There are other ways to do many of the things that people use paper space for. Often, the alternatives are simpler or more robust.

On the other hand, increasing use of paper space in many industries (notably the building design professions), paper space improvements in AutoCAD 2000, and the dependence of applications such as Architectural Desktop on paper space are forcing many of us to reconsider our paper space positions. I offer this analysis to spur your own thinking about how to incorporate paper space into your company's CAD procedures and also to help advance the ongoing discussion about appropriate use of paper space.

Paper space applications
The box below lists major paper space pros and cons, but when you're trying to build a consensus among advocates and detractors, pro and con arguments usually aren't productive. Those in favor tend to overvalue the pros and undervalue the cons, and vice versa. It's more helpful to think about how people use paper space, consider alternative methods, and then compare them, as shown in the table above. A rudimentary form of this analysis appears at May 2000 LT Online. If you engage in a similar exercise, you'll discover what makes the most sense for your company, based on the types of drawings you create, who needs to create them, and who needs to view or plot them.

Separate model, sheet files
I've encountered many production drafters who think that paper space is the only way to achieve a consistent 1=1 plot scale or to create a sheet of details that contains different detail scales (rows two and three in Table 1). Apparently many CAD users haven't yet learned how to separate drawings into model and sheet files, as shown in figures 1b, 2b, and 3b. Chapter 2, "Basic Organizing Concepts," in the AIA CAD Layer Guidelines, Second Edition, contains a good description of this approach for building drafting. You might choose not to adopt this method, but you should at least understand it (just as you should understand paper space, even if you don't use it for most drawings).

Figure 1. Paper space (a) and xref (b) methods to create 1=1 plot sheets.

To use the separate model and sheet files method in its purest form in AutoCAD, start by drawing each building plan, elevation, and detail in a separate model DWG file (in model space, naturally). You set up each of these model drawings for the scale of the individual view that you're drawing—there's no confusion caused by trying to draw at two or more different scales in the same AutoCAD drawing.

To create a plot sheet, you create a new DWG file and set it up, in model space, using a scale of 1=1 (that is, full scale, where 1 AutoCAD inch equals 1 plotted inch, assuming that you're working in inches). You xref, insert, or draw your title block and border, which appear at their true plotted size—for example, 36"X24" for an architectural D-size sheet. You then xref one or more files, using for each one an xref scale factor that's the inverse of the model file's drawing scale factor. See this January 2000 LT Online for more on drawing scale factor.

For example, you xref a 1/8"=1'0" building plan (drawing scale factor = 96) using 1/96 as the xref scale factor. This inverse scale factor reduces the model from real-world size to plotted sheet size. To show just part of the model, use the Xclip command to clip out any polygonal area (figure 3b). In the future, you open the model file to edit and open the sheet file to plot. You plot model space in the sheet file at a plot scale of 1=1, just as though you were plotting in paper space.

This method covers the vast majority of building drafting plot sheets. I find it simpler and more flexible than paper space in most situations. This method also seems easier to explain to people who aren't terribly AutoCAD-savvy.

Obviously, this method is based on the traditional 2D drafting methodology of drawing each view separately. 3D advocates will dismiss this method as based on a hopelessly antiquated approach to project documentation. Perhaps, but the technology in 3D building modeling and drafting tools is still fairly primitive. I question whether most companies are well-advised at this point to abandon a widely-understood and effective method of building documentation in favor of newfangled approaches that place very different demands on designers and drafters. But that's a subject for a future diatribe!

Figure 2. Paper space (a) and xref (b) methods for creating detail sheets.

Detail sheets
I especially like the separate model and sheet files method for creating detail sheets (figure 2b). It solves the "multiple scales on one sheet" problem without forcing you to resort to awkward paper space methods that depend on juggling different scales in model space and creating lots of viewports in paper space. When you create a detail sheet using separate model and sheet files, you follow the same rule of attaching each detail file at the inverse of its drawing scale factor and then plotting the entire sheet at 1=1. For example, you xref a 1"=1'-0" detail (drawing scale factor = 12) using 1/12 as the xref scale factor and a 3/4"=1'-0" detail (drawing scale factor =16) with 1/16 as the xref scale factor.

By keeping each detail in a separate file, you effectively create a library of modular, self-contained details, each of which you can paste on any drawing, copy to other projects, and manage as a separate component. You keep DWG file sizes small and make it easy for multiple users to work on details that appear on the same sheet. You also avoid AutoCAD performance problems that can result when you open a lot of viewports in paper space.

The main disadvantage of this method is that you end up with many more files. Good file-naming standards and organizing files into subfolders minimize this disadvantage, but it remains a big issue for some companies.

Figure 3. You can show different areas of the same model in several ways: (a) xref and paper space method, (b) xref and xclip method, or (c) paper space only method.

The paper space chase
If you've been grappling with when and how to use paper space, feel free to send me email with your current thinking and experiences. I continue to question whether paper space as standard operating procedure is the best approach for all companies. But it's certainly workable, and with the right CAD standards and training, it might be the best approach for some. It will be interesting to see how paper space use develops along with software and industry changes in the next few years.

Paper space pros and cons/Paper space uses and alternatives