Figure 7.1 Projection of a point7.4. Lines in Space
Lines can be thought as a series of points in space, having
magnitude (length) but not width. It will be assumed that a line
is straight unless otherwise stated. Though a line may be
located by establishing its end points and may be of a definite
specified length, all lines can be extended in order to solve a
problem. Therefore a purely theoretical definition of a line
could be: “Lines are straight elements that have no width, but
are infinite in length (magnitude); they can be located by two
points which are not on the same spot but fall along the line.”
When two lines lie in the same plane they will either be
parallel or intersect. Lines can be used to establish surfaces,
or solid shapes. In a majority of illustrations the view of a line
and its locating points are labeled with a subscript
corresponding to the plane of projection, as fig below where