hen oil workshops receive olives from an olive farm, they make oil. Clay pits take clay to pottery workshops, which produce pottery. Timber yards send their output to furniture workshops, which of course make furniture.

Oil, pottery and furniture all have two uses. You can export them for a profit, or hold onto them for local distribution through a market.

Your own citizens need pottery, oil and furniture before they will build really nice housing. Neighborhoods just stop improving until their residents can obtain these commodities from a nearby market. If your province can't produce pottery, oil and furniture, you will have to import them before housing can evolve to its full potential.