Houses will upgrade to the next quality level when the specific needs for their current level are met. This is called "housing evolution". These needs can be either commodities, services, or local desirability. The player is informed of the needs of any particular house, and so can act accordingly. Better overall housing quality benefits the city - not only better houses pay more taxes, but also draws in more people to the same residence, expanding workforce while saving space. It is often recommended to players to incentive housing upgrade instead of building numerous housing separately.