In order to generate a display of a surface, an equation or equations are generated corresponding to all or parts of the surface. The equation or equations represent the surface as a physical membrane. Boundary conditions of the surface can thus be specified, and the equation solved using the boundary conditions as outer constraints to generate a display of the surface. A set of points within the boundary of the surface may be specified, which then define inner constraints for the solution of the equation. Where parts of the surface join at a point or line, a further equation can be generated, which further equation represents the area around the join as a physical membrane. Solution of that equation, preserving the boundary of the area around the join, provides a smooth transition between the parts of the surface.