1. A computer implemented method of processing a gesture input on a touch screen display device, the method comprising: in response to receiving an invocation gesture on a touch screen display of the touch screen display device, displaying the annotation canvas as at least a partially transparent overlay on the touch screen display; receiving an input gesture on the touch screen display; when the input gesture is detected within the annotation canvas, interpreting the input gesture as an annotation gesture for inputting an annotation, and executing an annotation function associated with the input gesture within the annotation canvas based on the received annotation gesture; when the same input gesture is detected outside of the annotation canvas, interpreting the input gesture as a navigation gesture for moving an underlying graphical space to relocate the annotation canvas, and moving the underlying graphical space to relocate the annotation canvas, and displaying the annotation canvas on the touch screen display so long as the user's touch associated with the invocation gesture is maintained on the touch screen display, and stopping the display of the annotation canvas when the user's touch associated with the invocation gesture is removed from the touch screen display.