Doors are very important parts of transportation products as exemplified by the large number of them. In addition to doors for occupants to enter and exit there are doors for access to engine, cargo, luggage, air flow, fuel fill, etc.For transportation products, doors are usually designed to be flush with surrounding surfaces -- and most of them have hidden hinges . There are only a few mechanical alternatives to provide for the opening of doors and the use of simple pivoting hinges is predominant.There are two kinds of simple pivot hidden hinges -- in swinging and outswinging. These are named according to the initial motion of the edge of door with respect to its adjacent surface. Inswinging hinges are most prevalent for occupant entry/exit doors since they are required for most rear doors and they provide more pleasing cut line shapes for current surfaces, usually at lower cost.The door cut lines for hidden hinges which studio designers initially style on proposed products frequently cannot be achieved due to the inherent limitations. While achievable cut lines can be developed using trial -and- error methods, quicker and more reliable results together with a true understanding of the problems requires an analysis which identifies causes and simplifies their visualization. Such an analysis has led to a system for establishing the limits of surfaces and cut lines which has been named the “Volume-in- Space” method.It was developed originally for automotive occupant doors but is also applicable to other transportation items such as doors for luggage, engine, air flow, fuel, etc. as well as other pivoted parts such as convertible tops and aerodynamic suspension arms -- and even non- transportation hinged applications such as cabinets and machinery housings.As the top end view of a hinge center line for automotive occupant doors is observed, there are four basic limits to the volume in which the edge of the door must be contained. These limits are (1) the Swing-By Limit, determined by the requirement of the door swinging clear as it passes by the adjacent panel (or door) at initial movement, (2) the Molding Clearance Limit, determined by the requirement that any randomly located molding on the vehicle surface must not be contacted when the door is fully opened, (3) the Swung Limit, determined by the requirement that the door and the body parts must not contact each other when the door is swung fully opened, and (4)) the Inner Limit, determined by the most inward exterior surface possible with respect to the hinge on the door or other hardware in the door.By examining the parameters which affect each limit, projections can be made regarding ways of increasing the size of the limiting “Volume- in-Space”. Additional discussion is included on advantages for occupant entry/exit which have been gained in some products by orientating the hinge centerline at angles up to 4° from vertical. There are also opportunities for improving the door openings for both body structure and occupant entry/exit.