This study proposed a spatial power prior distribution for spatial mapping and hotspot findings in spatial data. The proposed prior distribution mines information from a finitely available historical data to elicit informative prior knowledge in the current spatial mapping task. It takes the relationship between the current and historical data into account, technically preventing the historical data from overshadowing the current inference. Spatial projection over the current study site was achieved using defined basis functions constructed with a finite element method given a triangular mesh representing the spatial domain. The proposed framework was applied to transcranial magnetic stimulation data to find the hotspot on a patient's scalp that produces the highest motor evoked potential.