Geographic Information Systems Flashcards

Which USGS topographic map scale provides sufficient detail for most project-level wetland delineations?

Answer: 1:24,000

The 1:24,000 scale (7.5-minute quadrangle) is the standard USGS topographic map series used for project-level field work and wetland delineations.

In GIS, a 'spatial join' is used in wetland analysis to:

Answer: Attach attributes from one layer to features of another based on location

A spatial join transfers attribute data from a source layer to a target layer based on spatial relationships, allowing wetland features to inherit attributes like soil type or land use.

The National Wetlands Inventory (NWI) uses the Cowardin classification system. In GIS, NWI data is delivered as which file format?

Answer: Shapefile or geodatabase feature class

NWI data from the U.S. Fish and Wildlife Service is distributed as vector shapefiles or geodatabase feature classes representing wetland polygons with Cowardin classification attributes.

A delineator uses a DEM to calculate flow accumulation. What does a high flow accumulation value at a location indicate?

Answer: Many upslope cells drain through that location, suggesting a potential drainage way or wetland

High flow accumulation values indicate that a large number of upslope grid cells contribute runoff through that point, identifying potential stream channels and wet areas.

Which metadata element is most critical to record when incorporating a GIS wetland data layer into a delineation report?

Answer: Data source, publication date, spatial accuracy, and coordinate system

Data source, date, accuracy, and coordinate system are essential metadata for evaluating data reliability and ensuring regulatory defensibility of the delineation.

When delineating wetlands from aerial photography, what is a key limitation of using only true-color (RGB) imagery?

Answer: It cannot distinguish between wet and dry areas with similar green vegetation color

RGB imagery lacks spectral sensitivity to soil moisture and plant water stress, making it difficult to distinguish wet vegetated wetlands from adjacent dry upland vegetation of similar color.

Which GIS operation would a delineator use to determine if a project area falls within a 100-year floodplain from FEMA FIRM data?

Answer: Spatial intersection or clip with the SFHA polygon layer

A spatial intersection or clip with the Special Flood Hazard Area (SFHA) polygons from FEMA FIRM data identifies which portions of a project area lie within the 100-year floodplain.