Sketch geometry behaves differently in a sketch, depending on the linetype assigned to it. In a part or assembly file, the sketch linetypes available are Normal, Construction, Centerline, and Reference.
In a drawing file, you have access to all the linetypes defined by the Drafting Standard you assign to the file.
This is the default linetype. Sketch geometry using Normal linetype is consumed by features.
Use construction geometry to constrain normal sketch geometry. It can aid in the development of sketches for parametric features. It is contained in the sketch, but does not add features when the sketch is consumed.
A variation of the Construction linetype, it is a visual aid in determining construction axes, or to dimension to a hypothetical location on the opposite side of the centerline and equidistant from the sketch geometry selected.
Reference linetype is assigned automatically to any sketch that is projected from a part edge. Reference geometry is associative, and updates automatically when the part face it is associated with is modified.
If you change reference geometry to another linetype, it loses its associativity.