Lay down blue Commercial zones to indicate where shops and offices can be built. This type of zone draws in profit for your city, though not as much as the Industrial zones, and provides jobs for your Sims.
Commercial zones provide Industrial buildings an outlet to sell their products, and a place for your Sims to spend their hard-earned Simoleans to buy happiness. However, if there aren't enough jobs, your residents will stay at home or go to a park rather than go out and shop with Simoleons they don’t have. No customers? No businesses.