Convention for labeling vertices of quadrilaterals.

Question

I am wondering if there is a convention for labeling the vertices of various quadrilaterals ABCD etc.

For example ABCD is a parallelogram. E is a point on DC extended, such that D and E are on opposite sides of BC.

Normally I put A in the top left then B in the top Right then C in the bottom left then D in the bottom right but it seems sometimes this results in incorrect construction.

Thanks!

Absent any explicit indications I would assume that the vertices of a polygon are labeled in consecutive (i.e. clockwise) order rather than in reading order. — user7530, Jan 01 '13 at 22:33

score 6 · Accepted Answer · answered Jan 01 '13 at 22:34

6

A common convention is that the vertices of a polygon are listed so that adjacent vertices are connected by edges. Thus the edges of quadrilateral $ABCD$ would be $AB$, $BC$, $CD$ and $DA$. So if it's a parallelogram, it might look like

A --- B          A --- D
 \     \     or   \     \ 
  D --- C          B --- C

answered Jan 01 '13 at 22:34

Robert Israel

448,999

1

Agreed, Robert. Usually I label counterclockwise because that is the positive orientation in the plane. – ncmathsadist Jan 01 '13 at 22:36

score 2 · Answer 2 · answered Oct 07 '15 at 10:26

2

I believe counterclockwise is the normal labeling convention - avoiding uncertainty as to what the polygon would look like.

answered Oct 07 '15 at 10:26

Charles Bowyer

41

Convention for labeling vertices of quadrilaterals.

2 Answers2