Variable speed image panning

A display apparatus is described having the capability to pan a viewport image across a world-plane image. The viewport image has defined boundaries and exhibits a cursor whose position is movable by a user operated mouse or keyboard controls. The invention comprises a method for providing a variable-rate pan action of the viewport image which includes panning the viewport image at a preset rate in the direction of a first viewport boundary, if the cursor has been moved to the first boundary. The viewport image is panned at a proportionally faster rate in the direction of the first viewport boundary, as the cursor is moved further beyond the first viewport boundary thus enabling a variable speed pan under user control.