Replace layers with classifications

[ML_Arco]

Layers and classifications serve a similar purpose, with layers being the older CAD-era paradigm and classification the newer, standard BIM way. It is somewhat of a nuisance that we still need to fill in and update both. For many long-term Archicad users, this seems like unnecessary double work and leads to confusion and neglect towards classifications, which means poor quality of models and extra work for BIM managers. 

I propose to replace layers completely with classifications in Archicad. View management could be done similar to Layer palette by checking and unchecking branches of the classification(s) that are in use, and saved into Classification combinations (like layer combinations). 

For compatibility with CAD import and export, some way of automated layer mapping would be required. Eg when importing from a format containing layers, Archicad could create a new (non-hierarchical) classification based on the layers of the original file, which would then enable controlling the visibility in the same way as described above. DWG translators could automatically export classification as DWG layers, with optional custom layer mappings (like now with Doors, Windows etc). 

For external drawings linked with the Drawing tool, nothing needs to be done - the embedded layers can remain as they are now (this is our preferred method of incorporating DWGs anyway). 

[ML_Arco]

Tags could be a nice additional way to organize and control the visibility of stuff. But we still also need proper (IFC) classification to ensure the exported IFC models can be reliably machine-read and used for further analysis, calculations, facility management and archival. As I understand, these tools rely on the classification to be able to recognize building parts, otherwise they just see unorganized geometry and data. Tagging stuff, possibly with multiple arbitrary tags wouldn't work for automating the conversion to IFC classes, so we would still need to do classifying too. The less extra work this requires from the user, the better.