In evaluation of the multifunctionality of agriculture and a rural community, some regular standardization of the evaluation means of the benefit for every subject has been performed. However, about the means of aggregating it to the total benefit, examination is not fully progressing. In many cases, the concept of area in which benefit can be aggregated, benefit area, is used for the aggregation means. However, there is almost no studies treated on it. So, in this study, we take up public project for reservoir in Osaka-fu, Oasis Project, and try to decide this benefit area. In fact, on the basis of Contingent Travel Cost Method, facilitation and elaboration of an aggregation are attained by using GIS. Finally we can describe the estimated result visually.