Simulation models may include a model of a space that is inhabitated by objects. One particular type of a space model is the two-dimensional discrete Euclidean space, called grid space. Due to their simplicity, simulation models based on a grid space have become popular in social science simulation. The wide adoption of the simulation framework NetLogo in social science simulation has contributed to the popularity of grid space models with fixed-increment time progression.
These models may still be considered DES models, even if they do not model any explicit events because their time steps may be viewed as implicit time events, similar to other periodic time events, like "every second", "each Monday", "at end of business week". Time events are a special category of events.
Whenever a grid space model does neither model objects nor events, but only grid cell states and grid cell state changes based on the states of neighbor cells, it may be considered a Cellular Automata model.
Examples of Grid Space Simulation Models with Fixed-Increment Time Progression
- Schelling Segregation Model: A residential area is populated by residents belonging to some group; periodically, all residents check if they are content with their neighborhood, based on their degree of tolerating neighbors of a different group; if they are not, they move to a location where they are content, or leave the area if they don't find such a location.
- Evolution of Microbes: The simulation model represents a small patch of a lake bottom. Microbes move across the screen living off a supply of bacteria. The bacteria are the only source of energy. The motion of a microbe is determined by a set of genes. The genes control the probability with wich a microbe will change its direction at a given time step.