Abstract
This paper examines the problem of describing an activity in a concise, usable way. An activity is defined by a vector of observed attributes. Including more observed attributes improves the explanatory power and theoretical completeness of any model of activities, but simultaneously leads to a combinatorial explosion when considering questions about choosing between activities, or sequences of activities, questions which arise in simulation applications. This paper first builds a description of individual activities using a vector of observed attributes. Then latent variable analysis is used to reduce this vector to just two latent variables, which together explain most of the variation in the original variables.