Question

Buffering operation on a point or a line results in a ________.

• A. Polygon
• B. Point
• C. Line
• D. Polyline

Hint:

A buffer is the set of all locations within a fixed distance of the input feature; think about what shape that set of locations traces out around a point and around a line.

Answer 1

The Correct Option is A

Step 1: Recall the definition of a buffer.
Buffering is a GIS spatial analysis operation that creates a zone of a specified distance \(d\) around a chosen input feature. The output buffer represents the set of all locations that lie within distance \(d\) of the input feature, so it is defined as an area, not as the original geometric type of the input.

Step 2: Work out the shape for a point input.
For a single point feature, the set of all locations within a constant distance \(d\) of that point is, by the basic definition of a circle, a disk of radius \(d\) centered on the point. This disk is bounded by a closed circular boundary line, which in GIS terms is stored and treated as a polygon feature.

Step 3: Work out the shape for a line input.
For a line feature, the set of all locations within a constant perpendicular distance \(d\) of any point along the line forms a band running parallel to the line on both sides, with the two ends usually rounded off by semicircular caps of radius \(d\) centered on the line's endpoints (a flat, square or round cap can be chosen, but the classic buffer uses rounded caps). This elongated band is a closed, two dimensional area, so it too is stored as a polygon feature, never as a line.

Step 4: Generalize and eliminate the wrong options.
Whether the input is a point, a line, or even a polygon, the buffer operation always outputs a two dimensional area bounded by a closed curve, because it answers the question "which locations are within distance \(d\) of the input", and any set of locations satisfying a distance condition around a point or curve necessarily fills out an area. The output can never be a lone point (option B), a single line (option C), or an open polyline (option D), since none of these represent an enclosed area of coverage.

Step 5: Conclusion.
Regardless of whether buffering is applied to a point or to a line, the resulting geometry is always a polygon.

\[ \boxed{\text{Polygon}} \]