If you’re just delving into the world of family creation, you probably have learned some intricacies of Revit, but there are many many unfathomable discoveries yet for you to behold! Here, I’ll help with one real quick. The all important Is Reference parameter of a reference plane is very often overlooked or improperly used.  Let’s go over it’s usefulness real quick.

Is Reference

1. Strong Reference
   
   Let’s say you have many Reference Planes in your family, and you want certain ones to be the first ones that your user’s cursor will snap to when dimensioning.  This is a strong reference.
2. Weak Reference
   
   OK, so you have some references that you want your user to be able to dimension to, but it’s not as important as the ones you’ve labeled as strong.  Weak reference will allow your user to snap to this reference plane with dimensions and other tools, but if it is near a Strong Reference, the user will need to tab to the Weak Reference.
3. Not a Reference – A reference plane marked as Not a Reference is the lowest hierarchy on snapping strength, and while it will allow a user to tab through to it, it till be the last of a a group to be selected if Weak or Strong references are in close proximity.
   
4. Top/Bottom/Left/Right/Front/Back
   
   These reference planes define the Left/Right (for example) extents of the family.  THIS DOES NOT DEFINE THE TOTAL EXTENTS OF THE FAMILY!!!!!  If you dimension one side of a family with Left/Right (for example) and click the witness line toggle square, the dimension will toggle between the center (see Is Reference explanation below) and the two side definitions.
   

   Also, if you use the pick walls tool while dimensioning, these Is Reference definitions will allow your family to report where the dimensions should go.
   

   

   It should be pointed out that these extend references function as Strong references when it comes to dimensions and will override Strong Reference for snapping purposes.

5. Center(Left/Right; Front/Back Elevation)
   
   Similar to the definition above, except this one deals specifically with the center definition of the family.  Does it have to be in the center?… nope.  Just remember that when you use this definition, the “center” option on the Pick Entire Wall Dimensioning tool will dimension to this Reference.

   Like the extent references above, these references will override Strong reference definitions for snapping purposes.

Well, I certainly hope that this was enlightening to a few of you.  I know it was an eye opener for me when I realized how powerful these Is Reference definitions were.  Thanks again fro stopping by and I look forward to seeing you next time for yet another, Revit TotD!

-Carl