Question

Select the CORRECT option that shows the match between Geometry and Error Type in vector data digitization.

Geometry
(P) Tiny graphic polygons
(Q) Open polygons
(R) Overshoot/undershoot
(S) Polygons with inadmissible loops

Error Type
(1) Sliver polygon
(2) Dangle
(3) Weird polygon

• A. P-1; Q-2; R-2; S-3
• B. P-2; Q-2; R-1; S-3
• C. P-2; Q-1; R-2; S-3
• D. P-1; Q-3; R-2; S-2

Hint:

Separate the errors into two families: ones caused by a duplicated/misaligned boundary line (sliver polygons) and ones caused by an unconnected line end (dangles); a self-crossing boundary is a weird polygon.

Answer 1

The Correct Option is A

Step 1: Recall how a sliver polygon is created.
A sliver polygon is a spurious, very thin and small polygon that appears when the same real world boundary, shared by two adjacent features, is digitized twice with slightly different coordinates, for example once in each of two overlapping layers, or twice along a common edge. The tiny gap between the two nearly coincident lines is registered by the software as its own closed area, which shows up as a tiny graphic polygon. So tiny graphic polygons (P) are caused by the sliver polygon error, giving P-1.

Step 2: Recall what a dangle is.
A dangling node, or dangle, is a node connected to only one line segment instead of at least two. It is produced whenever a line that should meet another line, or should close back on itself, fails to do so properly. An overshoot happens when a digitized line runs past the intersection point it should stop at, and an undershoot happens when it falls short of reaching the intersection, both leave one end of a line unconnected, that is, a dangling node, giving R-2. In the same way, an open polygon is a polygon boundary whose start and end points do not coincide, so the boundary line has a free unconnected end, which is again a dangling node, giving Q-2.

Step 3: Recall what a weird polygon is.
A polygon whose boundary line crosses over itself, forming a self intersecting or bowtie shaped loop, is not a simple, well formed polygon. Because its geometry violates the normal rule that a polygon boundary must be a simple closed curve that does not cross itself, this abnormal, inadmissible-loop shape is termed a weird polygon, giving S-3.

Step 4: Assemble and verify.
Putting the four matches together gives P-1, Q-2, R-2, S-3, which is exactly the combination listed in option (A). Every other option either assigns tiny graphic polygons to dangle instead of sliver, or assigns open polygons to sliver instead of dangle, both of which contradict the standard definitions above.

\[ \boxed{\text{P-1; Q-2; R-2; S-3}} \]