over 4 years ago - Avanya - Direct link
Specialised industries produce the raw materials generic industry uses to make goods, which are in turn used by commercial. Offices do not need goods. The regular offices just provide jobs, while the IT offices produce some goods.

You don't technically need industry in your city, and if you have enough IT offices, you can supply your commercial with that. But if commercial needs more goods, they will import instead, which costs them more than local goods would, meaning less tax for you.

You can use the "Outside Connections" info view on the panel on the left to see which buildings import (or export) to see if you are fulfilling your city's needs locally or if some import is needed.