Understanding Parameter differences in Revit

As part of my upcoming presentation on  Global Parameters - "Power to the People" (Session 1.4 at 3.15pm) at RTC NA in Scottsdale, Arizona on 14 July 2016 I did a lot of research on exactly how each kind of parameter works in Revit.  It is a lot more complicated than I first thought (even though I knew from experience it was not simple).

I thought I would share some of my findings here, as they could be useful for reference generally - regardless of whether you are using Global parameters or not.  I will be referring to some of this research in my presentation, but won't have time to go into detail as the main focus will be the exciting possibilities Global Parameters.

Understanding Different Kinds of Parameters in Revit

System Family built-in Parameters – these are properties that are hard-coded into Revit software, and can be used where available. They can usually be scheduled and sometimes tagged, but not always. They can apply as instance (&/or type) data to:

• system families: walls, floors, ceilings, stairs, railings etc
• Project info
• View and sheet parameters
• Areas, Rooms and Spaces

Custom family custom parameters – user defined (type or instance)

Custom family built-in parameters – system defined (type or instance)

Project Parameters – exist only in the project; user defined; have to be assigned to categories, and hence to families; and cannot include calculations

Shared Parameters – derived from an external master list; can be scheduled and tagged

• can be used for Family (custom) or project parameters, but not for Global or system/built-in parameters

Global Parameters – exist within a project; allow calculations outside the family

Reporting Parameters – extract a length or angle from a model, for use in calculations within families or global parameters; have many limitations within custom families

Calculated Value - these are properties (not real parameters) created within a schedule or tag family (from Revit 2017) - they can include formulas or just be static values for use in other formulas or scheduling;  they are not available anywhere else except the schedule or tag that they are created in.

Key Schedule Parameter - a special kind of schedule can be created that works like a lookup table;  a very few built-in parameters can be included in a key schedule, in which case they are available for tagging;  user created key schedule parameters cannot be Shared Parameters, which makes them of very limited usefulness.  If this latter functionality could be fixed, then Key Schedules would become a very important part of Revit, instead of languishing in the backwaters of arcane uselessness.

The Matrix

There are many limitations and inconsistencies in the way that each type of parameter works in Revit. Here is a matrix (or two) to help to understand the differences: