Join Paul F. Aubin for an in-depth discussion in this video Organizing with categories vs. layers, part of Migrating from AutoCAD to Revit.
One of the most critical aspects of success in Revit is achieving a firm grasp of how Revit organizes data. This is not hard to do when you consider that the organization of elements in Revit is actually quite logical and very consistent. Frankly, for most new users the issue has more to do with the need to unlearn existing AutoCAD habits, rather than a difficulty in understanding Revit fundamentals. One such fundamental is the difference in object organization. AutoCAD uses layers to manage data. Revit has no layers, and instead uses categories.
But the two are far from equal. So, let's take a look at some of the differences. In AutoCAD, with the exception of layer 0, layers are user defined. That means that you can create your own layers, rename them, delete them as project needs dictate. But categories in Revit are completely built into the software. They can't be added, they can't be renamed, and they can't be deleted. So here in Revit, I'm in a file called Condo Unit, and if you already have this file open, you might want just close and reopen a fresh copy without saving. I'm going to go to the Manage tab, and we can see a list of all the categories in Revit by using the Object Styles command.
Now, when I click on Object Styles, it opens up this dialog, and you could see it's organized into the tabs and the first tab is the Model Objects categories. Now here, you're going to find all of the various architectural objects. We've got things like Casework, Ceiling, Columns, Doors, Windows, you name it. So, if I select one of these items like the first one on the list, the Casework category, you'll notice that there's no place here where I can rename or delete or remove or even reorganize this category. All of that is built in.
The only thing I can't change is things like as Line Weight and its Color and its Pattern, which is a little bit similar to the things we can do in AutoCAD. So, let me cancel out of here for a second and unlike AutoCAD where when you draw elements, you have to specifically think about which layer those elements need to be placed on, that's not really the case here in Revit. If I highlight an existing object, you'll notice that the first item says the category. This one's the Walls category. If I highlight this, it says this is the Doors category.
If I highlight this, it says it's the Furniture category. And if you go and add new elements, there is no way that this new wall could be anything but a wall. There's no way that this new door could be anything but a door. It's not possible to create a door element and put it on the Windows category. It just simply can't be done. So in AutoCAD, the layers primarily define the graphical characteristics, similar to what we just saw in Revit. We could change the Line Weight or the Color or the Line Pattern.
Now in Revit, it goes much deeper than that. As we saw just a moment ago, when you create a new element in Revit, it knows which category to go to because the category fundamentally defines the nature of that element. It can't be anything else. It's not possible to put it somewhere else. So it defines it, not only where it goes but, its fundamental behaviors and characteristics, and this is why when you draw two walls, they know how to join with one another, and when you create a door, it knows how to cut a hole in the wall, because all of those behaviors are built into part of that category.
Layers are also used not only to control the graphical characteristics, but also to control the visibility. But this is done globally across the entire drawing. If you turn off a layer in AutoCAD, that layer goes off everywhere. But in Revit, visibility is view by view. So, if we take a quick look over here in Revit, what you can see is we can use categories to turn objects on and off just like we can with layers in AutoCAD, but in Revit it's going to be done on a view by view basis. So, for example, let's say that in this view, I no longer wanted to see any of the furniture.
So, what I would have to do is go to the View tab and choose a slightly different command, Visibility Graphics. Now, when this first opens up, it looks pretty similar to the dialog we were in a moment ago except that now you'll see there's a small check box next to each of the categories and with this check box, I can turn off a particular category in the same way that you can turn off a layer in AutoCAD. So, you'll notice that if I open up another Floor Plan, the furniture is still turned on here.
So yes, we can use the categories to turn objects on and off, but it's not a global setting. It applies to each individual view, which gives us a little bit more power and flexibility. The final difference that we want to look at between layers and categories is that layers are nonhierarchical. There's no such thing as a sublayer. When you create a layer in AutoCAD, it is just a flat list of layers. So, if you wanted a door panel layer and a door swing layer, and you wanted those related to the door layer, you really have to just be clever with naming and clue in the team members to use them that way.
But in Revit, we actually can have subcategories and those categories are nested underneath their parent categories. So, if we take a look at that, I'm going to go back to Object Styles, and you'll notice a small Plus sign next to each of the categories. So, we've got various subcategories that are built in part of the software, and if I look at doors here--because that's a pretty common example--you can see that we've got things like Elevation Swing and Glass and panel.
Maybe I want the Plan Swing category to graphically look a little bit different here in this view. Notice that we've got several different kinds of doors on the screen. I've got a single swing door. I've got a double swing door. I've got a bi-fold door. Well, some of these different doors, even though they're completely different kinds of doors, have door swings. So, if I want to make a change to those door swings across all of those doors, I can use Object Styles for that. So, I'm going to do really simple example here and just change the color, and let's click Apply and notice that regardless of the kind of door, all of the swings have turned red in this case.
If you've been using AutoCAD for a while, it's uncomfortable at first trying to get used to working without layers. However, once you begin using Revit, you quickly discover that not having to worry about the layer as your work is actually quite refreshing. It won't be long before you find yourself quite happy to leave your layers behind.
- Comparing AutoCAD and Revit
- Customizing Revit settings
- Exploring the Revit interface
- Organizing with categories versus layers
- Understanding families and groups versus blocks
- Using links instead of Xrefs
- Tracing, nesting, and exploding CAD files