Simulation involves creating an artificial system to represent the behavior of a real system. In geographic information science, this involves (a) systems in which location is a critical component and (b) the use of computer programs as the means of representation. In common usage, simulation refers to the iteration of procedures as a means of either representing the passage of time or finding a solution to a difficult problem. The purpose of simulation may be simply to observe the behavior of the artificial system for the purposes of understanding more about the behavior of the real one (commonly referred to as modeling), or it may be to address a specific problem that cannot be solved analytically (i.e., with mathematical formulae).