A question

What exactly is a 'wart factory'?

I'm only asking because Thomas Thiis-Evensen apparently thinks that Karl Johan Street* looks like one. Oh, I'm sorry, only parts of it. Which parts, I wonder? Where does the wart factory begin, where does it end?

All these questions ...

*Oslo's main street, named after King Carl XIV Johan of Sweden and Norway (1818-44, the 'bedchamber regime' ... he was a total hypochondriac.)