An on-board vehicle control system and method employ a storage device that stores information representing a plurality of boundary points of a boundary circumscribing an area of interest in which the boundary points are defined by two prescribed parameters, and a controller that obtains at least one condition point defined by current values of the prescribed parameters, determines a first boundary point of the boundary points that is closest to the condition point, and generates geometric data representing a geometric relationship between the first boundary point, the condition point and a second boundary point of the boundary points. The controller performs further calculations taking into account the geometric data to generate coordinate condition data, and determines whether a warning condition exists by determining whether the condition point lies within the area of interest based on a comparison between coordinates of the condition point and the coordinate condition data.