Abstract : Geospatial Decision Support Products (GDSPs), computer-based tools that help interpret geospatial data, are ubiquitous within current military forces. Although GDSPs are used widely, and are generally perceived as useful, there is too little empirical evidence to assess the value of GDSPs to the warfighter. Achieving a better understanding of the potential value of GDSPs while they are still in development would help to prioritize scarce intellectual, physical, and monetary resources, and would result in having the most valuable GDSPs available to the warfighter. General experimental methods are well understood and have been used recently to evaluate GDSPs during development (e.g., Powell et al., 2009). However, it can take considerable time and effort to recruit the type and number of participants required to conduct experiments with adequate statistical power. This paper describes how formative evaluations emulating experiments in terms of hypotheses, scenarios, procedures, and measures, but using only a small number of subject matter experts (SMEs), can be used effectively to inform development decisions about the potential value of GDSPs. A case study in which a formative evaluation was used to inform development decisions for the Battlespace Terrain Reasoning and Awareness-Battle Command (BTRA-BC) Tactical Spatial Objects (TSOs) is presented to illustrate the method.