CWD Geographic Information Systems 2 — Questions and Answers
Question 1: Which GIS data model is most appropriate for representing continuous wetland water table depth across a landscape?
- Vector polygon layer
- Raster grid layer (Correct answer)
- Point feature class
- Network dataset
Correct answer: Raster grid layer
Raster grids store continuous spatial data as a matrix of cells, making them ideal for representing gradients like water table depth across a landscape.
Question 2: What does NDVI stand for in the context of remote sensing used for wetland mapping?
- Normalized Difference Vegetation Index (Correct answer)
- National Digital Vegetation Inventory
- Natural Drainage Vegetation Indicator
- Normalized Data Validation Index
Correct answer: Normalized Difference Vegetation Index
NDVI (Normalized Difference Vegetation Index) measures plant greenness using near-infrared and red spectral bands and is widely used to identify vegetated wetland areas.
Question 3: A delineator needs to identify hydric soil boundaries using aerial imagery. Which spectral band combination is most useful for distinguishing wet soils from dry soils?
- RGB true color only
- Near-infrared and shortwave infrared (NIR-SWIR) (Correct answer)
- Ultraviolet and visible blue
- Thermal infrared only
Correct answer: Near-infrared and shortwave infrared (NIR-SWIR)
NIR and SWIR bands are sensitive to soil moisture content, making them the most effective combination for distinguishing wet hydric soils from dry upland soils.
Question 4: In a GIS topology, which relationship ensures that wetland polygons in a layer do not overlap each other?
- Must Not Have Gaps
- Must Not Overlap (Correct answer)
- Must Be Covered By
- Must Contain Point
Correct answer: Must Not Overlap
The 'Must Not Overlap' topology rule validates that no two polygon features share interior area, ensuring clean, non-redundant wetland boundaries.
Question 5: Which coordinate system is recommended by the U.S. Army Corps of Engineers for mapping wetlands at a local project scale in the contiguous United States?
- Geographic coordinates (WGS84 decimal degrees)
- State Plane Coordinate System (Correct answer)
- World Mercator
- Polar Stereographic
Correct answer: State Plane Coordinate System
State Plane Coordinate System provides high accuracy for local and regional mapping in feet or meters and is commonly used for project-scale wetland delineations.
Question 6: When using LiDAR data to support wetland delineation, what derived product best reveals subtle topographic depressions that may hold water?
- Hillshade
- Digital Surface Model (DSM)
- Topographic Position Index (TPI) or depression fill analysis (Correct answer)
- Contour lines at 10-foot intervals
Correct answer: Topographic Position Index (TPI) or depression fill analysis
TPI and depression fill analysis identify closed low points in a bare-earth DEM, highlighting microtopographic depressions where water pools and wetlands form.
Question 7: A GIS analyst clips a national wetlands layer to a project study area boundary. The original data is in NAD83 and the study area is in WGS84. What should be done before clipping?
- No action needed; NAD83 and WGS84 are identical for practical purposes
- Reproject both layers to the same coordinate reference system (Correct answer)
- Convert the wetland layer to a shapefile
- Change the map scale to 1:24,000
Correct answer: Reproject both layers to the same coordinate reference system
Although NAD83 and WGS84 are very similar, they are technically distinct datums and must be projected to the same CRS to ensure spatial alignment and accurate geoprocessing results.
CWD Geographic Information Systems 2
Which GIS data model is most appropriate for representing continuous wetland water table depth across a landscape?