Layer filters are a great tool to organize the many layers that are created by an AutoCAD user. The drawback to Layer filters is that they do increase the size of the DWG file. I had a friend send me a DWG file once that was 2 MB in size. The DWG contained only one line, drawn on layer 0 and had been purged and audited of any blocks or errors. The reason for the large file size, was that he had roughly 800 Layer filters.
Layer filters are associated with objects or blocks. If a block is set to a layer that is in a Layer Filter and the block is copied from one drawing to another, the Layer filter will also be copied over. To remove all the layer filters within the over-sized drawing, I used an old LISP routine called LAYERFILTERSDELETE.
Autodesk has now recognized that layer filters have become more of a problem then a useful tool. Therefore, with the release of AutoCAD 2006, a new system variable is available that will automatically delete layer filters when the drawing contains more that 100 of them.
The system variable is LAYERFILTERALERT. With this variable, you have better control on when and if layer filters should be deleted. By default, this variable is set to <2>. The following outlines what all the options do:
0 - Off
1 - When Layer Manager is open, deletes all filers, mo message is displayed
2 - When Layer Manager is open, displays a message that states the problem, recommends deleting all filters and offers a choice.
3- When the drawing is opened, displays a message that states the problem and offers to display a dialogue box where you can choose which filters to delete.