When an application requires a user to choose an object from a presentation space, the user typically selects the object by positioning the mouse cursor over the object and clicking the mouse buttons. This action sends a message to the application, informing the program of the current (X,Y) position of the mouse cursor. However, it is still up to the application to determine the object selected. This is accomplished by the application defining a rectangular area called the "pick aperture," which is centered on the reported mouse position, and determining which, if any, of the currently defined segments intersect or lie completely within the pick aperture. The process of determining intersection or inclusion within the pick aperture is called "correlation."