Underlay Action – Slice, Slice, Baby

So, I’ve found myself with some lovely time spent working through the joys of Underlays.  We just had some confusing goings ons, and I thought I would try to get to the bottom of it.

Underlays can be very useful for figuring out what is going on above and below.  And on top of that, any Linework tweak you do to an element in an Underlay, will stay on when you turn the Underlay off!  That’s the kind of thing that gets a geek excited!

From a previous event, I decided I should spend more time in the Help docs, to see if that could lead me the right way.  This was the most important thing the Help File had about how they work:

Displays another slice of the model under the current plan view. That slice of the model can be from above or below the current level. The underlay appears dimmed and is visible even in hidden line. The underlay is useful to understand the relation of components on different floors. Normally, you would turn off the underlay before exporting or printing the view. You set an underlay by specifying a level. The slice of the model between that level and the next level up displays. Three of the underlay options (Current Level, Level Above, and Level Below) are relative to the current level. All other choices are absolute. See Halftone/Underlay.

So not much.  Had to crack open Revit and play for a while.

I would like to preface, this is all based on minutes and minutes of vast experimentaiton.  If someone can point me out as wrong, PLEASE DO.  I would love to know this stuff.

First off – Underlays don’t show linked models.  I tried copy/monitor levels, tried messing with Visibility Graphics, no way could I get a linked model elements to show in an Underlay.  It just didn’t exist as far as the Gods of the Underlay were concerned (Hades, Pluto, Osiris).

Next up is a clarification of the Help File.  Both setting the Underlay and the Underlay’s own view range are dependent on levels… but they MUST be levels that have a floor plan or RCP associated with it.  I’ll clarify.

When you go to select what Level you want for the Underlay, only levels with plan views will show in the list.  In the below snapshot, you see the dropdown for Underlay only showing “Level “1 and “Level 2” (and “None”), when clearly the elevation indicates Level 4, Level 5 and Roof.  Level 4, Level 5 and Roof have no plan or RCP associate with them.  If I were to create a plan, then that level would show up in the list.

The Help File also indicates that the “slice” of what the Underlay shows is from the level you select to the level above that level.  The Help File does NOT indicate that the “level above” must have a plan associated with it.

So, in the example above, if “Level 1” is selected as the Underlay, the “slice” will go from Level 1 to Level 2.

If “Level 2” is selected, then the “slice” will go from Level 2 to… infinity… or wherever Revit decides to stop the model.  I didn’t test this.  I simply put a wall 100′ above Level 2 and it did indeed show up when the Underlay was set to “Level 2”.

As soon as a plan or RCP are created for a level above Level 2, then the “slice” will shrink.  If that plan or RCP is deleted, then the “slice” will grow again.

So, I would propse the Help File be tweaked.  First of all, get rid of that line about “Three of the underlay options (Current Level, Level Above, and Level Below) are relative to the current level.”  I don’t even think that’s an option.  Beyond that:

The slice of the model between that level and the next level up, with an associated plan view, displays.

And maybe add a picture of me giving someone a high five while actually drinking Slice.  That would be cool.  Does that drink even exist anymore?  Now I’m thirsty…

2 thoughts on “Underlay Action – Slice, Slice, Baby

  1. Matt says:


    In revit 2011, how do you disable the selection for underlays? It is anoying you are trying to select an wall which is in the same position as the one underneath.

    Also how do you make the current layers walls more prominent. The underlay interferees with the clarity of selecton.


  2. jkunkel says:

    Sadly, as far as I know, there is no way to not select the underlay. It is there “live” for all actions.
    To make your current layer walls more prominent, you would either tweak your Object Styles (which would impact your entire project) or modify your Visibility Graphics in that specific view.

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