I have a base category tree with around 10000 nodes.
Now there are several thousand cities, every city has various categories as based in the base category tree but not all of the categories existing in the base category.
Quite a lot of categories are shared between cities but some of the categories are not shared between them.
I do not need something like STI as they would make categories unique for a particular city. And as there are many cities which would have the same categories, would also need a new category node.