(see illustration at the beginning of this article), Gandy portrayed the building as a picturesque ruin in order to show the internal plan arrangement, a precursor of the cutaway view. A montage image is produced by superimposing a perspective image of a building on to a photographic background. Care is needed to record the position from which the photograph was taken, and to generate the perspective using the same viewpoint. This technique is popular in computer visualization, where the building can be photorealistically rendered, and the final image is intended to be almost indistinguishable from a photograph. Sketches and diagrams A sketch is a rapidly executed freehand drawing, a quick way to record and develop an idea, not intended as a finished work. A diagram could also be drawn freehand but deals with symbols, to develop the logic of a design. Both can be worked up into a more presentable form and used to communicate the principles of a design. In architecture, the finished work is expensive and time consuming, so it is important to resolve the design as fully as possible before construction work begins. Complex modern buildings involve a large team of different specialist disciplines, and communication at the early design stages is essential to keep the design moving towards a coordinated outcome. Architects (and other designers) start investigating a new design with sketches and diagrams, to develop a rough design that provides an adequate response to the particular design problems. There are two basic elements to a building design, the aesthetic and the practical. The aesthetic element includes the layout and visual appearance, the anticipated feel of the materials, and cultural references that will influence the way people perceive the building. Practical concerns include space allocated for different activities, how people enter and move around the building, daylight and artificial lighting, acoustics, traffic noise, legal matters and building codes, and many other issues. While both aspects are partly a matter of customary practice, every site is different. Many architects actively seek innovation, thereby increasing the number of problems to be resolved. Architectural legend often refers to designs made on the back of an envelope or on a napkin. Initial thoughts are important, even if they have to be discarded along the way, because they provide the central idea around which the design can develop. Although a sketch is inaccurate, it is disposable and allows for freedom of