GIS For Engineering (MCQ) 4 — Questions and Answers
Question 1: Which geoprocessing tool is used to extract a smaller dataset by overlaying a polygon boundary on another dataset, keeping only features inside the boundary?
- Intersect
- Clip (Correct answer)
- Erase
- Dissolve
Correct answer: Clip
Clip cuts input features using a polygon boundary, retaining only the portions of input features that fall within the clip boundary.
Question 2: An engineer must model underground utility networks in 3D. Which GIS data format supports true 3D geometry with Z coordinates and topology?
- Shapefile (.shp)
- Geodatabase with multipatch features (Correct answer)
- GeoJSON
- CSV with lat/lon
Correct answer: Geodatabase with multipatch features
ESRI File Geodatabases support multipatch and PolylineZ/PolygonZ feature classes that store true 3D geometry with topological rules enforced.
Question 3: What is a Digital Elevation Model (DEM) primarily derived from in modern large-scale engineering surveys?
- Satellite multispectral imagery
- LiDAR point clouds or SAR interferometry (Correct answer)
- Topographic map digitization
- GPS waypoint grids
Correct answer: LiDAR point clouds or SAR interferometry
Modern high-resolution DEMs are primarily derived from airborne LiDAR point clouds or spaceborne SAR interferometry (InSAR), which provide dense elevation measurements across large areas.
Question 4: In a GIS attribute join, what happens when multiple records in the join table share the same key value as a single feature in the target layer?
- All matching records are appended as new features
- Only the first matching record is joined (one-to-one join) (Correct answer)
- The join fails with an error
- An average of numeric fields is calculated
Correct answer: Only the first matching record is joined (one-to-one join)
A standard attribute join performs a one-to-one match; when multiple join table records share the same key, only the first match is used unless a relate or spatial join is applied instead.
Question 5: Which statement correctly describes the difference between raster resolution and raster extent?
- Resolution is the total number of cells; extent is the cell value range
- Resolution is the cell size (e.g., 1 m/pixel); extent is the geographic area covered (Correct answer)
- Resolution defines the CRS; extent defines the resampling method
- They are synonymous terms for pixel size
Correct answer: Resolution is the cell size (e.g., 1 m/pixel); extent is the geographic area covered
Raster resolution refers to the ground dimension represented by one pixel (e.g., 30 m/pixel), while extent defines the geographic bounding box of the entire raster dataset.
Question 6: What is the purpose of a rubber-sheeting operation in GIS?
- Converting vector data to raster format
- Distorting a dataset to align it with a more accurate reference layer using control points (Correct answer)
- Stretching raster contrast for visualization
- Snapping vertices to a grid
Correct answer: Distorting a dataset to align it with a more accurate reference layer using control points
Rubber-sheeting uses control point pairs to warp (stretch and bend) a dataset so its features align with a spatially accurate reference layer, correcting systematic positional errors.
Question 7: Which SQL spatial function would an engineer use in PostGIS to find all buildings within 500 meters of a fault line?
- ST_Intersects(buildings.geom, fault.geom)
- ST_DWithin(buildings.geom, fault.geom, 500) (Correct answer)
- ST_Contains(fault.geom, buildings.geom)
- ST_Envelope(fault.geom)
Correct answer: ST_DWithin(buildings.geom, fault.geom, 500)
ST_DWithin returns true when two geometries are within a specified distance of each other, making it the correct function for proximity-based queries in PostGIS.
GIS For Engineering (MCQ) 4
Which geoprocessing tool is used to extract a smaller dataset by overlaying a polygon boundary on another dataset, keeping only features inside the boundary?