Coordinates are vital for many aspects of any Revit project. In fact, coordinates are a part of every Revit project, whether you intentionally interact with them or not. In most smaller projects, and even sometimes in bigger projects you may not even worry about coordinates… at least not that you intentionally think about. But there is one area of every project you do interact with coordinates, and that is with Levels. In a Level’s Type Parameters, you have the ability to set the “Elevation Base” to either Project Base point, or Survey point.
The default location of the Project Base Point is in the same place as Revit’s Origin (or 0,0,0). If you move it, let’s say down in the Z axis, the elevation dimension on the Level will change (assuming of course, the Level’s Elevation Base is set to Project Base Point.)
note: previous to Revit version 2020.2 the functionality was the same, you just had to unclip the Project Base Point before you moved it.
This comes in handy when you need to set the construction datum to something other than 0’-0”. For example, if you want this to read 100’-0”, you simply move the Project Base Point down 100’ and voila!
If you edit the Level’s Type Parameters and change the “Elevation Base” parameter to Survey Point, the Level’s dimension will instead read based on the location of the Survey Point … Maybe!
This is where there is confusion, and you DON’T EVEN REALIZE IT! The truth is the dimension shown on the level is not actually using the Survey Point as its reference. The Level is actually using the current Shared Coordinate! If you move the Survey point (just as you did the Project Base Point), but leave it clipped, you are also moving the Shared Coordinate location, and in this scenario everything seems to be copasetic and working as intended.
BUT if you unclip the Survey Point, then move it, the location of the Shared Coordinate does not change and neither does the dimension of the Level! So, in fact, the Level’s dimension is not reading from the Survey Point as advertised! It’s actually reading from the the Shared Coordinate location.
This probably doesn’t make a difference in most Revit projects, and you may have never even dealt with this. But you might get frustrated or confused and think something is “broken” if you ever need to set the Levels to read from the “Survey point”, then unclip the survey point and move it to another location.
By the way, the same hold true for the Spot Elevation and Spot Coordinate dimensions!