Boundary points are points from the definition of boundaries, which are automatically created when boundaries are created. One bound-ary point is designed for each vertex of the boundary geometry. Each boundary point has one property named series representing an association of the boundary point to a sensor, which becomes a context sensor (described later). The association is defined by selecting a sensor from a boundary point popup interface within a specified distance to the boundary. The length for possible sensor association is also defined in this popup interface.