Interaction Model

The player is almost always multipresent in a CSG because the designer has decided the player needs to see what is happening all over the game world. (Minecraft, as usual, is an exception, but in its creative mode the avatar can fly, making it effectively multipresent.) It’s difficult to control a large-scale process from the inside, where you can’t see everything that’s going on. Most CSGs don’t give the player any kind of avatar. However, players do like to see what the worlds they’re building look like from the inside, so sometimes games implement a walkthrough mode that lets players walk around the world in a first-person perspective. Walkthrough mode is entertaining and the player will enjoy it, but the primary interaction model in a CSG needs to be multipresent if there are large-scale processes to be managed.

Camera Model

The camera model in a CSG naturally depends on what you are simulating. Many CSGs simulate a process taking place over a land area—whether it’s a city, a farm, or an entire planet. As a result, these games tend to use an isometric perspective. The early games were all tile-based, and some still are on smaller devices, but for the most part, modern CSGs now use 3D environments. This has the advantage that players can zoom in and out and move the camera freely, which lets them see a broad overview most of the time, then focus on a local problem when one arises.

If your game simulates a process taking place in a three-dimensional space, you might find it useful to divide the space into layers to make it easier for the player to navigate around the game world. It’s also helpful to provide a button that returns the camera instantly to a default perspective so that the player can reorient himself if he gets lost.

User Interface

Because CSGs aren’t trying to create an illusion of reality in the way that first-person shooters or flight simulators do, their UIs can be more computerlike, using pull-down menus and rows of buttons along the edges of the screen. CSGs emphasize convenience over verisimilitude. Different audiences prefer different amounts of information on their screen, so be sure to play-test your game with your intended audience to be sure they can find the information they need. (Generally speaking, children and older adults prefer screens that are less information-dense.)

In a CSG that is based on an internal economy, the player learns to understand and control a mathematical model—although that’s not the way you will present it to her. She needs convenient access to key variables within the model. You should display the most important scalar variables (single-value variables)—for example, the amount of money she has to work with at the moment—on the screen at all times. The display can show digits if that’s most appropriate or a bar graph or some other kind of graphic device, depending on the nature of the simulation.

Often the player needs to know not only the current value of a variable, but also how that variable has changed over time. This lets her track and respond to trends before trouble occurs. In Theme Park, visitors come into the park, spend time, and leave again. The player can see them wandering around but has difficulty getting a sense of the park’s popularity just by counting heads. The player can bring up a graph to see how the population has changed over the past 1, 3, or 12 game years.

With vector variables (multivalued variables), you need a different approach. In Caesar, for example, the player builds a Roman town. Every area of the town needs a water supply of some sort, whether a well, pipe, or fountain. The amount of water available throughout the town is a vector variable, having a separate value for each square on the town grid. The game’s default perspective shows all the buildings, water wells, fountains, and so on, but it makes it difficult for the player to visualize exactly which areas are served by water supplies. To get a clearer picture, the player can bring up a different view of the game world that hides all the buildings except for the water supplies and shows a blue overlay over the rest of the town. The shade of blue in each area indicates the amount of water available there, from light blue indicating little water to dark blue indicating plenty.

You must provide the player with these kinds of analytical tools so she can learn what’s going on inside the simulation. SimCity supplies several types of overlays that inform the player about fire danger, crime, pollution, and so on. These tools allow her to locate trouble spots quickly and to respond. These kinds of map overlays should not be snapshots that freeze a moment in time, but rather they should be updated continuously by the simulation. That way the player can watch them for a while and tell whether particular situations are getting better or worse—and most important, whether her actions are having the desired effects. Don’t provide so much data that the game turns into a dry simulation, however. Part of the fun of FarmVille is in figuring out the best crop to plant. The game should give the player enough power to deduce the best way to play, but it shouldn’t tell her the best way explicitly.