GIS Spatial Analysis Methods 3 — Questions and Answers
Question 1: What is the main difference between a raster overlay and a vector overlay in GIS?
- Raster overlays require topology while vector overlays do not
- Raster overlays combine cell values mathematically while vector overlays create new geometric intersections (Correct answer)
- Vector overlays are faster to process than raster overlays
- Raster overlays can only handle two input layers at a time
Correct answer: Raster overlays combine cell values mathematically while vector overlays create new geometric intersections
Raster overlay applies map algebra to combine pixel values, while vector overlay geometrically intersects features to create new polygons with combined attributes.
Question 2: In geostatistics, what is a 'nugget' in the context of a semivariogram?
- The maximum semivariance at large distances
- The range at which spatial autocorrelation disappears
- The semivariance at zero distance, representing measurement error or micro-scale variation (Correct answer)
- The sample size used in variogram estimation
Correct answer: The semivariance at zero distance, representing measurement error or micro-scale variation
The nugget is the y-intercept of a semivariogram model, representing variability at distances smaller than the sampling interval or measurement error.
Question 3: Which type of spatial analysis would best identify retail locations that are underserved by existing stores?
- Hotspot analysis
- Service area analysis (Correct answer)
- Terrain analysis
- Morphological analysis
Correct answer: Service area analysis
Service area analysis delineates the geographic reach of existing stores, allowing identification of areas beyond current service coverage.
Question 4: What does a negative Moran's I value indicate about a spatial dataset?
- Perfect spatial randomness
- Positive spatial autocorrelation (clustering)
- Negative spatial autocorrelation (dispersion) (Correct answer)
- An error in the spatial weights matrix
Correct answer: Negative spatial autocorrelation (dispersion)
A negative Moran's I indicates negative spatial autocorrelation, where dissimilar values tend to be located near each other (checkerboard pattern).
Question 5: In the context of raster analysis, what is 'focal statistics'?
- Statistics calculated for the entire raster extent
- Statistics computed for each cell based on values within a defined neighborhood (Correct answer)
- The process of resampling rasters to a common resolution
- Statistical comparison between two raster datasets
Correct answer: Statistics computed for each cell based on values within a defined neighborhood
Focal statistics calculate output values for each cell using a moving window or neighborhood of surrounding cells, such as focal mean or focal maximum.
Question 6: Which method is most appropriate for interpolating precipitation data collected at irregularly spaced weather stations?
- Nearest neighbor resampling
- Kriging (Correct answer)
- Euclidean allocation
- Tabulate intersection
Correct answer: Kriging
Kriging uses statistical models of spatial correlation to provide optimal unbiased predictions at unsampled locations, making it well-suited for environmental variables like precipitation.
Question 7: What is the purpose of using a Thiessen (Voronoi) polygon analysis in GIS?
- To create buffers of variable width around line features
- To assign every location to its nearest point feature (Correct answer)
- To smooth elevation data across a landscape
- To detect spatial clusters of disease incidence
Correct answer: To assign every location to its nearest point feature
Thiessen polygons delineate regions where every location within a polygon is closer to that polygon's seed point than to any other seed point.
GIS Spatial Analysis Methods 3
What is the main difference between a raster overlay and a vector overlay in GIS?