In Real-time Strategy (RTS) Games, players often have to gather resources from specific spots in a level that we will call “expansion”. The action of taking an additional expansion will be called “expanding”. To do so, they need to invest their current resources to gather more. By resources, I specifically mean the ones present in the games such as “Metal” in Planetary Annihilation or “Minerals” in Starcraft but it can be more creative as we will see later.

The economies are different in every RTS game and every variation has an impact on the level design. What we are interested in here is how much freedom there is in the positioning of expansions depending on the parameters of the economy. There are multiple layers that create restrictions on level design such as factions. They are not relevant here because it’s a layer of restrictions that comes later in the design of an RTS game. In this article, we assume the game has only 1 faction which has only 1 combat unit.

The economy in numbers

There are 4 main parameters in a RTS game economy: 

There are other values outside the economy that are useful to normalize the parameters seen above. This will let us compare different games.

Why use median? There are games with units or structures that greatly stand out from the rest by having large amounts of health or damage compared to the others. These units often appear in the very late stages of the game so they have a minimal impact on the ability to expand. Medians are less affected by extreme values.

From these 4 values of an economy, there are multiple metrics that are useful: 

The risk of expanding

Now we have these numbers, it’s time to discuss the concept of risk of expanding. In RTS games, you have 3 options to spend resources:

When the player is spending resources to increase the income, he is not building additional units. And so, there is the risk that he can lose the game because he invested too much into expanding his economy and he simply didn’t have enough units to defend an attack. The risk of expanding is based around this dynamic.

We can create a risk score from the previous metrics. It will allow us to see, in any RTS game, how risky it is to expand and how much freedom there is in the placement of expansions.

There is another effect of risk score that is not related to level design but that is worth mentioning. It also affects the strategic depth of the game. It means how meaningful the choice between expanding, building combat units or teching up is. In a game with a low risk score, players can expand and build combat units at the same time so there is less diversity in the player’s choices. While in a game with a high risk score, the choice between expanding and building combat units is important and it creates more diversity in strategies. 

To find the risk score, I decided to attribute a score to the time ROI, time Destroy and ratio Cost and then add them together. By doing so, the 3 metrics below become equally important in the risk score. The brackets of the values are decided based on the largest values found in the games that can be seen later. 

Now we have the formula, let’s use it in some example games.

Planetary Annihilation

Risk score = 1 + 1 + 5 = 7