Construction Geometry
You can convert sketch entities in a sketch or drawing to construction
geometry. Construction geometry
is used only to assist in creating the sketch entities and geometry that
are ultimately incorporated into the part. Construction geometry is ignored
when the sketch is used to create a feature. Construction geometry uses
the same line style as centerlines.
Any sketch entity can be specified
for construction. Points
and centerlines are always construction entities.
The SolidWorks software also
has Reference
Geometry (planes, axes, and so on) as a basis for creating features
outside of sketches.
To convert sketch entities to construction
geometry:
In an open sketch, select one or more sketch entities and do one
of the following:
Select For construction
in the PropertyManager.
Click Construction
Geometry 
on the Sketch toolbar.
Click Tools, Sketch
Tools, Construction Geometry.
Right-click a sketch entity and select Construction
Geometry (drawings only).