Understanding Revit element hierarchy

- In this movie I'm gonna expose you to some of the high-level organization and hierarchy that's built into the Revit software. It's important to understand how all of the different objects and elements in the Revit platform fit into a broader structure, so we'll start at the top level and we'll kind of work our way down. So, every element in Revit is part of a category, those categories are built into the software and they come from a fixed list. Beneath those categories we can have subgroupings and we call those groupings "families", and then those families can either be subgrouped even further into "types", and then finally we have the objects themselves that we can select in our projects and our models.

Now, going back to the top level, the category level, those categories break down into certain sort of overall groupings that Revit understands that are very important to impart certain basic functionality into the objects. Now, I like to call these groupings "buckets" because I don't really have a better word for them, but there's really a few major groupings. We have our model elements, we have our view-specific or annotation elements, and then we have some special-case elements like the view elements and the datum elements.

So, let's talk first about what the difference is between, say, a model element and, on the opposite end of the spectrum, say, an annotation element. A model element is quite simply anything that represents a real thing, so if you think about the building when it's all done and you walk out with your hard hand and you actually can put your hand on it and touch it then it was a model element. So that would include things like these walls over here, things like these doors over here, this stair and railing, those are all model elements, they physically exist, you can put your hand on 'em and touch 'em. The behaviors of all the model elements that they share in common is you create them in any view and they show in all views.

We saw examples of that in the previous movie. So if you make a change to a model element in one view you can be very confident that it's gonna change everywhere. The model elements are drawn full size, actual size, full scale. So those are some of the characteristics of model elements. On the opposite end of the spectrum we can contrast that with many view-specific elements, and what I mean by view-specific elements is these are elements that belong specifically to the view, but specifically I'm talking about annotation elements. Now, there's lots of different kinds of annotation elements, we have things like dimensions, we have things like this bar scale right here, this North arrow, these labels and tags.

All of those things are necessary for architectural communication but they're not real elements, nobody paints the dimensions or the bar scale or the tags on the floor of the building, they're not actually physical objects. Furthermore, those objects only exist in the view that they're created in. So, notice that I'm in a level one floor plan view right here, and it has several room tags, several wall tags, door tags, it has dimensions. There's lots of different annotation elements. Well, I also have a level one power plan, and if you look at it you'll notice that the layout is exactly the same because it's got the same walls, the same doors, the same windows, but notice that it has very different annotation, there's only a couple dimensions, the room tags are outside the rooms and they're in totally different locations.

Now, we saw in the previous movie that if we, say, zoom in right here and I grab this door and I move it over here that we're gonna expect to see that change occur in all places throughout the model, and in fact it does, the door has moved in any version of this floor plan. However, if I took this quarter tag right here and I move it over here, and then I go back to the level one power plant, this room tag is unchanged because in fact they are two different room tags because they're view-specific.

Now, in other reason why that's the case is because annotation elements or view-specific elements respond to scale. So this view is set to 1:100, when I change the scale none of the model geometry will change but all of the annotation will. So if I change it to 1:50 notice that all of the tags have just gotten smaller but of course all of the model geometry remains exactly the same. So, that's the sort of major "buckets", right? And the difference between model and annotation is a pretty big distinction, and keep that in mind as you work in Revit because you're gonna see those behaviors again and again, and the more you understand how they behave the more you can begin to predict things in the Revit environment.

Now, another really important hierarchical concept is the concept of category-family-type. So I mentioned it briefly but let me dig into it a little bit more in detail. The categories are built into the software, so they're things like walls, doors, windows, tags, dimensions, these are all categories, and they just impart certain behaviors and features on all of the elements in our Revit project. Now, talking about walls is a pretty broad category, talking about doors is a pretty broad category. If we think about a door, a door is hole in a wall that we can pass through, but doors come in all sorts of shapes and sizes and kinds.

So, right here on the screen I have a single door and a double door, those are pretty different from one another even though we recognize them both as being doors. Well, the difference between this single door and this double door would be what we would call a "family" in Revit. So a family is a little bit more specific designation and it defines much more specific characteristics than just the broad grouping of the category. Another example is furniture. All of these items here are furniture but a desk is very different than a chair, which is very different than a credenza.

All of them are considered furniture, they're part of the furniture category, but the desk, the chair and the credenza are different families. Now, even within each family you often have variations and those are called "types". So if I took this door right here and come over here to this list you'll notice that it actually has several different variations. Now, the types describe really just different sizes, so I could drop this door to a different size and in all ways is very similar to the other doors within the same family, but now it's just a slightly smaller size.

So by working you way down from category to family to type you progressively get more and more specific on the kinds of things that you can change, but one of the important characteristics to understand is that all objects at the same tier of the hierarchy share common characteristics. In other words, if you change something about this type it would affect all other instances of that type, so this door right here, this is exactly the same type right here, if I made a change to that type this one would be affected as well. If I made a change to the family both of these doors would be affected, even though they're different types.

And then, of course, if I made a change at the category level it would affect all doors including this one out here. So, the hierarchy basically tells us at what level are modifications going to take place, are they gonna affect only the object we have selected? Are they gonna affect a group of objects? Or they gonna affect an entire category of objects? And we get to decide what those behaviors will be and how far-reaching our edits are made just in the choices we make and in understanding how that hierarchy in Revit functions. So, as we go through the course we'll be seeings plenty of examples of that and we'll get plenty of opportunities to learn the specifics of why we might want to dig in and make changes at all those various levels.