Area average rainfall estimation is important to determine the exact amount of the available water resources and the
essential input data for rainfall-runoff analysis. Like that, the necessary criterion for accurate area average rainfall estimate is
the uniform spatial distribution of raingauge network. In this study, we suggest the spatial distribution evaluation
methodology of raingauge network to estimate better area average rainfall and after the suggested method is applied to Han
River and Geum River basin. The spatial distribution of rainfall network can be quantified by the nearest neighbor index. In
order to evaluate the effects of the spatial distribution of rainfall network by each basin, area average rainfall was estimated
by arithmetic mean method, the Thiessen’s weighting method and estimation theory for 2013’s rainfall event, and evaluated
the involved errors by each cases. As a result, it can be found that the estimation error at the best basin of spatial
distribution was lower than the worst basin of spatial distribution.