Question

Consider the three input raster images given below. A geospatial analyst decided to use the overlay operation to generate a new raster showing the average values. The values of the cells P, Q, and R in the output raster are:
Input raster
 

5	2	3
1	2	2
3	1	1

→

1	3	2
4	7	5
1	1	1

→

3	4	1
4	3	2
2	1	1

Output raster

 

P	Q	R
-	-	-
-	-	-

• A. \( P = 3, Q = 3, R = 2 \)
• B. \( P = 4, Q = 4, R = 3 \)
• C. \( P = 3, Q = 3, R = 3 \)
• D. \( P = 4, Q = 4, R = 2 \)

Hint:

In raster overlay operations involving arithmetic like averaging, apply the function cell-by-cell across the input rasters. Double-check each individual cell position across all rasters to avoid errors in indexing.

Answer 1

The Correct Option is A

To compute the value at each cell in the output raster using the average overlay operation, we take the corresponding cell values from each of the three input rasters and compute their average. Let us compute: 
- \( P \): Top-left cell of the raster. \[ P = \frac{5 + 1 + 3}{3} = \frac{9}{3} = 3 \] - \( Q \): Top-middle cell of the raster. \[ Q = \frac{2 + 3 + 4}{3} = \frac{9}{3} = 3 \] - \( R \): Top-right cell of the raster. \[ R = \frac{3 + 2 + 1}{3} = \frac{6}{3} = 2 \] Hence, the output values are: \( P = 3, Q = 3, R = 2 \)