Generating Elevations - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 510

4. To complete the lines representing different heights in the elevation,
copy the three horizontal roof lines down 1 ′ -11 ″ (584 mm).
These will be the lines at the edge of the roof where it covers the
pop-out (see Figure 10.5; note that two of the lines appear to be at
the same height). Use a crossing selection window to select the lines;
be sure not to select the line representing the tops of the windows.
Copy these three lines
Do not copy this line
To here
FiGuRE 10.5 The horizontal height lines for the elevation in place
Each of these lines represents the height of one or more components of the
cabin. Now you'll drop lines down from the points in the floor plan that coincide
with components that will be visible in the elevation. The south elevation will
consist of the exterior walls, two windows, the pop-out, and the roof.
using Construction Lines
to Project Elevation Points
In addition to the standard LINE command, AutoCAD offers two additional types
of lines: rays and construction lines . As you know, to create a standard line, you
must define both a starting and ending point for the line. Construction lines
have neither a starting nor an ending point, and extend to infinity in both direc-
tions. Rays are a mix between standard and construction lines; having a starting
point but no end point.
Both rays and construction lines can be trimmed in much the same way as
standard lines. Since by definition a construction line is a line of infinite length,