The size of your lawn, the throw of the heads, the run time, the number of heads per zone and overlap between their spray patterns, the amount of sun and evaporation during watering, and the water pressure at each head all together determine the answer to your question.
You can twiddle all of these factors except the size of the lawn. A pump is one way to control one of these factors. If you do what you can with all the rest and find that you need an excessive number of zones, maybe a pump will be necessary. There are calculator tools for this.