GIS Spatial Analysis Methods 5 — Questions and Answers
Question 1: What is the primary difference between interpolation and extrapolation in the context of spatial analysis?
- Interpolation uses vector data while extrapolation uses raster data
- Interpolation estimates values within the range of sampled data while extrapolation estimates beyond it (Correct answer)
- Interpolation is more accurate than extrapolation in all cases
- Extrapolation requires fewer sample points than interpolation
Correct answer: Interpolation estimates values within the range of sampled data while extrapolation estimates beyond it
Interpolation predicts values at unsampled locations within the convex hull of the data, while extrapolation extends predictions to areas outside the sampled extent.
Question 2: Which GIS operation would you use to calculate the total area of forest within each county polygon?
- Clip
- Dissolve
- Tabulate intersection (Correct answer)
- Merge
Correct answer: Tabulate intersection
Tabulate intersection calculates the area (or length/count) of one feature class that falls within each feature of another, making it ideal for area summaries by zone.
Question 3: In terrain analysis, what does a 'flow accumulation' raster represent?
- The slope gradient at each cell location
- The cumulative number of upstream cells draining into each cell (Correct answer)
- The direction water flows out of each cell
- The total precipitation received by each watershed
Correct answer: The cumulative number of upstream cells draining into each cell
Flow accumulation counts the number of upslope cells that contribute flow to each cell, with high values indicating stream channels or drainage convergence zones.
Question 4: What is a 'spatial weights matrix' used for in spatial statistical analysis?
- Storing the geographic coordinates of sample points
- Defining which locations are considered neighbors and how much influence they have on each other (Correct answer)
- Converting attribute data from one projection to another
- Weighting raster cells by their area in acres or hectares
Correct answer: Defining which locations are considered neighbors and how much influence they have on each other
A spatial weights matrix formally encodes neighborhood relationships between spatial units, specifying which features are neighbors and the strength of those connections.
Question 5: Which spatial analysis method would be most appropriate for predicting housing prices across a city based on a sample of known sales?
- Nearest neighbor analysis
- Geographically weighted regression (GWR) (Correct answer)
- Quadrat analysis
- Reclassification
Correct answer: Geographically weighted regression (GWR)
GWR fits local regression models at each location, allowing relationships between variables to vary across space, which is ideal for spatially non-stationary phenomena like housing prices.
Question 6: In raster analysis, what is the key characteristic of 'zonal statistics'?
- It calculates statistics using a moving neighborhood window
- It computes summary statistics for cells within defined zones from a separate zone layer (Correct answer)
- It applies global statistics to all cells equally
- It measures connectivity between raster cells
Correct answer: It computes summary statistics for cells within defined zones from a separate zone layer
Zonal statistics calculates summary statistics (mean, sum, max, etc.) for values in one raster within each zone defined by a separate zone raster or feature class.
Question 7: What problem does the 'edge effect' cause in spatial analysis, particularly in point pattern studies?
- Raster cells at the edge of a dataset have lower resolution
- Features near study area boundaries have fewer potential neighbors, biasing distance-based statistics (Correct answer)
- Vector features are automatically clipped at the study area boundary
- Edge cells are excluded from all spatial calculations
Correct answer: Features near study area boundaries have fewer potential neighbors, biasing distance-based statistics
Edge effects occur because features near boundaries have neighbors beyond the study area that are unobserved, causing distance-based analyses to underestimate clustering near edges.
GIS Spatial Analysis Methods 5
What is the primary difference between interpolation and extrapolation in the context of spatial analysis?