How Many Layers Do You Really Need?
Last month in the LinkedIn ArchiCAD Group, Timothy Ball started a discussion entitled “Generating Correctly Named Layers – UK,” which got me thinking again about layers. He advocated naming layers according to Uniclass, a UK industry standard comparable to CSI’s UniFormat in the US. In my quest for interoperability, I once used UniFormat as the basis of my own layering system. However, it proved to be impractical given the large number of layers used and to be incomplete given the small number of categories accommodated. Even with 287 layers, it accommodated only 23 categories of building elements—after factoring in related layers to coordinate element display with renovation status, separate projections, and annotations. A pitiful outcome compared to 612 similar categories in UniFormat 2010. Then Graphisoft introduced the renovation filter, which helped a bit. But after reading John Maeda’s Laws of Simplicity, the realization hit me: the best use for layers in ArchiCAD was to provide a filter of last resort for controlling elements in 2D projections of the model (i.e., plans, elevations, and sections). That insight reduced my template to 21 layers.
“So, what can you do with just one layer—the mandatory, always-on, ArchiCAD Layer?”
Start Simple
Using only the ArchiCAD Layer, layer combinations are useless for controlling elements in 2D projections. But ArchiCAD 16 provides other tools for this purpose, such as story settings, individual element settings (including sections and elevations), and ArchiCAD’s other built-in document filters (model view options, renovation filter options, partial structure display, pen sets, and floor plan cut planes). The available model output is enough for schematic design in general and even construction documents on a simple project (although you might need a couple 2D worksheets for the electrical plans):
- Site Plan
- Floor Plans
- Roof Plan
- Interstitial Plans (with a few caveats)
- Elevations
- Sections
- Interior Elevations
- 3D Documents
- Schedules and Lists
When annotation requirements are minimal, interstitial plans showing concealed structural and/or mechanical elements can be modeled using the model view options to render the floor slabs transparent and the partial structure display to hide non-load bearing elements. Alternatively, 3D documents can be used to create similar drawings from the model, regardless of annotation requirements. Otherwise, draw other plans and details independently of the model using the 2D worksheet and detail tools. Here are some tips and limitations:
- Place site elements on a separate story.
- Display overhead objects as dashed elements on the floor plan.
- Model elements and annotations share the same layer.
- 3D elements shown in elevation and/or section also appear in plan (subject to partial structure display settings).
- 2D elements may be added in one view without appearing in others.
- Only modeled elements can appear in schedules or lists, which excludes 2D objects inserted into elevations, sections worksheets, or details.
- Visual conflicts will likely arise in trying to model electrical fixtures in plan without additional layers, which will prevent creating an electrical fixture schedule from the model.
- To control where objects such as trees and furniture appear pay special attention within object settings to the 3D detail level and floor plan display.
- Objects appearing in the 3D window and hence 3D documents may be selected individually and/or by using the Find & Select tool. Rules for selection criteria can be created, edited, and named for future use, but updates must be performed manually.
Multiply Your Power: Alternates
To explore alternate schemes, add one layer and one layer combination for each alternate and restrict the ArchiCAD Layer to shared elements.
ArchiCHAZZ 
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While I do see the value of the Layers inside ArchiCAD, I was thinking along similar lines: we want to add info to objects to control their listing, their visibility and the info they carry along in e.g. IFC.
Layers are an old concept and flawed in one major area: it is a uni-dimensional list (vector) where each object can sit on only one layer. When you use layers to provide functional information, you need as many layers as you have functions. When you use layers to also provide phasing information, you have to multiply the amount of functions with the amount of phases to cater for all possible combinations. In practice you need less, but each and every possible additional use for layers you add will quickly increase the amount of layers that are required.
In traditional CAD systems, this was almost the only way to category entities, so you often had 60+ or 100+ (or more) layers.
In ArchiCAD you have much more options for “tagging”: layer, tags (position, structure, all IFC fields), ID, story, renovation status (alas, only three possible states).
Interesting blog post and valuable idea. I would not dismiss layers, but better understanding how to use them will improve our thinking and the organization in our BIM models.
Revit doesn’t need layers because it provides other means to tag objects and add information. A little more flexible, but harder to get to grips with.
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This criteria is more than perfect, thank you.
PS: I can understand Timothy Ball’s methodology in relation to Uniclass, it’s because there is no direct way in ArchiCAD (which I´m aware of) to create CAD layers based on Uniclass’s element classification system, but there is a work around using schedules.