Their ability to consider multiple independent criteria in evaluating the acceptability of a given policy strategy does not require the heroic assumptions necessary for formulating an aggregated welfare function in policy optimization models. Because the algorithms applied by policy guidance models are similar to those of optimization models, they also require a highly simplified representation of dynamic system components. Optimizing models either apply global averages or distinguish a limited number of geopolitical regions. Most policy evaluation models, in contrast, determine climate impacts on a geographical grid (often 0.5° latitude by 0.5° latitude).