GIS Spatial Analysis Methods 4 — Questions and Answers
Question 1: What is 'map algebra' as used in raster GIS analysis?
- A method for projecting maps into different coordinate systems
- Mathematical operations applied to raster layers on a cell-by-cell basis (Correct answer)
- The process of digitizing paper maps into vector format
- Statistical analysis of attribute tables in GIS
Correct answer: Mathematical operations applied to raster layers on a cell-by-cell basis
Map algebra performs mathematical and logical operations on raster grids at the individual cell level to create new output rasters.
Question 2: Which spatial analysis technique would you use to determine how many customers live within a 10-minute drive of each store location?
- Quadrat analysis
- Network-based service area analysis (Correct answer)
- Standard deviation ellipse
- Spatial autocorrelation
Correct answer: Network-based service area analysis
Network-based service area analysis follows road network topology to calculate travel-time zones around facilities, unlike simple Euclidean buffers.
Question 3: In spatial statistics, what does a high G-statistic (Getis-Ord Gi*) value indicate?
- A cold spot — cluster of low values
- A hot spot — cluster of high values (Correct answer)
- A random distribution of values
- Significant spatial outliers
Correct answer: A hot spot — cluster of high values
A high positive Gi* statistic indicates that a location and its neighbors have significantly higher values than the global average, forming a hot spot.
Question 4: What is the 'modifiable areal unit problem' (MAUP) in spatial analysis?
- Difficulty in projecting circular features into planar coordinates
- Statistical results that change depending on how areal units are defined or aggregated (Correct answer)
- Errors introduced when converting raster to vector data
- The problem of assigning point data to grid cells of varying sizes
Correct answer: Statistical results that change depending on how areal units are defined or aggregated
MAUP refers to how spatial analysis results can change significantly depending on the size and shape of the zones used for aggregation.
Question 5: Which spatial relationship operator would select all parcels that share a boundary with a flood zone polygon?
- Contains
- Within
- Touches (Correct answer)
- Intersects
Correct answer: Touches
The 'Touches' spatial relationship selects features that share a boundary or endpoint but whose interiors do not overlap.
Question 6: What is the main advantage of using a weighted overlay versus a simple raster overlay in site suitability analysis?
- Weighted overlay is faster to compute
- Weighted overlay allows different criteria layers to contribute unequally to the final result (Correct answer)
- Simple overlay is more accurate for continuous data
- Weighted overlay eliminates the need for data reclassification
Correct answer: Weighted overlay allows different criteria layers to contribute unequally to the final result
Weighted overlay lets analysts assign importance percentages to each criterion layer, reflecting real-world priorities in the suitability score.
Question 7: In point pattern analysis, what does a nearest neighbor ratio (R) value less than 1.0 indicate?
- A dispersed or regular pattern
- A random spatial distribution
- A clustered pattern where points are closer together than expected (Correct answer)
- Insufficient data points for analysis
Correct answer: A clustered pattern where points are closer together than expected
An R value less than 1.0 means the observed average nearest neighbor distance is shorter than expected under randomness, indicating spatial clustering.
GIS Spatial Analysis Methods 4
What is 'map algebra' as used in raster GIS analysis?