In this chapter, we introduced the essential elements of an internal economy: resources, entities, and some of the mechanics that manipulate them, including sources, drains, converters, and traders. We examined the concept of economic shapes as seen through graphs and showed how different mechanical structures can produce different shapes. Negative feedback creates equilibrium, while positive feedback creates an arms race among opponents. Implemented another way, positive feedback can produce a downward spiral, because a player finds it harder and harder to grow his economy. Feedback systems based on relationships between two players can produce effects that keep games close or tend to cause the player in the lead to stay in the lead.
Game designers can use internal economics in many ways to make games interesting, enriching both the progression of a game and the strategic choices a player has to make. The internal economy also affects the competitive landscape between diverse or closely matched players in multiplayer games. The chapter ended with specific suggestions about how to build games in which players construct an economy, as in SimCity.