This paper describes our Mobile Spatial Interaction (MSI) prototype MobiSpatial, which benefits from location and orientation aware smartphones and existing open source spatial data initiatives to facilitate user interaction with the geospatial query process. We utilize today's ubiquitous mobile device as the central computing platform to calculate a mobile user's visibility shape at his/her current location. MobiSpatial uses this shape as a query "window" in a spatial database to perform line-of-sight, field-of-view and 360° Isovist visibility searches. These visibility based spatial queries reduce the risk of "information overload" by exploiting "hidden query removal" functionality to retrieve only those objects that a user can actually see. By incorporating open source datasets and databases, our application manages to store, index, query, retrieve, and display spatial information solely on the mobile device itself, without concern for any server side computations or internet connections.