Well I thought there were two different 'author-group': the first makes only single scenarios and the second makes campaigns.. It is pretty cool that campaign-makers make also some maps for the single scenario
I have also thought that some of the single scenarios are made by fan, because there are so much maps and it is hard to imagine that all of them are made only by 5-10 people who work in NWC / 3D0
Not all people know, but some spells have different probabilities of appearing in different town types. Examples:
- Ice spells will never appear in Inferno
- Armageddon never appears in Rampart, Castle, or Tower
- Rampart is most likely to get Dimension Door
- Teleport is most common in Fortress
- Hypnotize doesn't appear in Necropolis
- Antimagic is most common in Stronghold