The line directly underneath the side windows of the car, the junction of the upper greenhouse and the lower bodyside or shoulder.
Emphasis may be given by the addition of a bright strip or by a change in body section which will produce a more subtle running highlight
The position and inclination of the beltline not only affects the appearance and proportion of a car, but also its character and stance. A car with a low beltline - and therefore tall greenhouse - may look 'delicate', elegant or modern. A car with a high beltline, and correspondingly shallow greenhouse, will tend to look tough and mean.
A rising beltline provides the long-fashionable 'wedge' appearance and imparts a dynamic sense of purpose and direction.
UK English: Waistline
A vertical slice through a car body side which is then viewed at 90 degrees to help understand or appreciate the form. Tape lines applied to the surface show a section nicely, the trailing edge of an open front door describes it perfectly, but only at that point - body sections are rarely constant.
A simple glance at typical body sections will reveal that most have convex main surfaces, although creases and feature lines may introduce local negative contrasts. It was the introduction of unexpected 'negativity' on BMW's principal surfaces that caused such a reaction to Chris Bangle's 'flame surfacing'.
The lateral line at which the maximum width of a car can be measured (excepting door mirrors).
It may be created by a crease or any of the main body section lines, but for practical purposes it is usually designed to be an applied body side protector moulding or rubbing strip.
The current fashion is to avoid added body side protectors, with the body wide line defined by a more subtle body crease.
(See also swage line, feature line, crease, character line)
There can be a fine line between some of these terms, and this has led to a certain conversational 'interchangeability' of terminology, and to some loss of their true meanings and origins. Though not structural per se, all have an important primary function in reinforcing body panel stiffness and reducing vibration. They will, however, be part of the visual structure of a car.
Their principal purpose is to variously create definition, add emphasis, visual interest, design organization, and to direct - or even deceive - the viewer's eye.
A bone line is a hard, positive only, linear 'peak' in a car's bodyside, more prominent than a crease line.
To contrast with the often-used 'taut skin over muscle and sinew' metaphor, this implies sheet metal, similarly stretched, but over something more structural (see haunch).
An interesting, or unique, bone line can also be a character line eg. 2000 Toyota Celica, Mercedes CLS.
