Abstract – Pointwise geological data in are used as initial information for creating hydrogeological models (HM). Interpolation methods are applied to create -maps on (xy)grids of HM. The maps represent geometrical and physical features of geological layers. If solutions of boundary field problems are used as interpolation results then in represent boundary conditions. They must be joined to nodes of the interpolation grid. In this paper the case is considered when the local data search region presents a circle. Features of this approach are investigated if the circle radius changes from zero to two plane steps of a uniform (xy)grid.