Base datum coordinates and making it work with linked in other files, like DWG and RVT, isn’t the easiest thing to get your head around. I have been using Revit for over 10 years and it is still a mystery to me. For new projects, I never get it right first go. I have to have a couple of stabs at it before the coordinates are all set right and everything links it correctly. Visibility of the coordinate controls isn’t super easy. And it has changed in Revit 2021. One change which will be handy is; Coordinates of linked files visible: To more easily coordinate linked files, you can see the survey point, project base point, and internal origin of linked models in the host model
By default, the project base point and the survey point display only in the site plan view. The Internal Origin is off by default in all views. You can make them visible as needed.
You can display the project base point 
, the survey point 
, and the internal origin in all types of 2D and 3D views. For cropped views, you may need to resize the crop region to see the points.
- Open the desired view.
- Click View tab > Graphics panel > (Visibility/Graphics).
- On the Model Categories tab of the Visibility/Graphics dialog, scroll down to Site, and expand it.
- To display the project base point, select Project Base Point.
- To display the survey point, select Survey Point.
- To display the internal origin, select Internal Origin.
When there are linked models present, the project base points 
,the survey points 
, and the internal origin 
are shown in gray.
To temporarily display the project base point, the survey point, and the internal origin in a view, on the View Control Bar click 
(Reveal Hidden Elements).
It is possible for 2 or more coordinate points to be in the same position. Symbols for coordinate points in the same position will overlap. For example if the project base point and the survey point are in the same position it will look like this:
