Why can't I delete empty layers in TBC?

This question comes up quite a bit and the answer can be found here.

While a layer in TBC may look like it is empty - i.e. I isolate the layer and zoom extents and the extents displayed are a small area and there is no data visible - so the assumption is that the layer is empty and therefore should be possible to delete if it is unprotected - Right? / Wrong …

The reason that the layer is still retained can be for any one of the following reasons

  1. The CAD files that you import will typically include AutoCAD Blocks. Those blocks are placed on one layer but when they were defined can contain data (Lines, Text, Points etc.) that reside on other layers. So when in TBC and you isolate the layer that the block is placed on, you will see all of the content of the blocks, making you feel that all the data is defined on the same layer, that is incorrect. In the same way you look at the layers where the block contents are defined and they make look empty, that is also incorrect. The layers are empty until you explode the block, at which point all the block content is returned to their own defined layers, and so the block content layers are not seen by TBC as empty because they are required for the block contents when exploded.

  2. The CAD files that you import also are derived typically from either AutoCAD or MicroStation. Those systems have two areas for data - the Model Space (equivalent of TBC Plan and 3D Views) and Paper Space (Equivalent to TBC Sheet View). So when you import a CAD file that has both Model Space and Paper Space data included, the Model Space data maps to the plan view and the Paper Space data maps to Plan Sets, Sheet Sets and Sheets in TBC. The Plan Sets will show up in the Project Explorer in TBC and will often use layers that may show nothing in the plan view that only become visible in the Sheet View - so while in the Plan View the layer may appear empty, it may in fact contain data in the Sheet View that you would have to delete if you want to clean out the “empty” layers. If you do not need the Paper Space information, you can delete the Plan Sets and Sheet Sets from the project Explorer and then try to delete the empty unprotected layers and you should find that they will delete provided that there are no Blocks that reference the “empty layers”.

So Explode the Blocks (and you may need to explode 2 or more times because Blocks from CAD files can be nested multiple times, so a single explode may not be sufficient, and delete the Plan Sets from the Project Explorer and then you can likely eliminate those annoying empty layers from the project.