GIS Geospatial Data Fundamentals 4 — Questions and Answers
Question 1: What is the purpose of a datum in a coordinate reference system?
- To define the units of measurement for map coordinates
- To define the origin and orientation of the coordinate system relative to the Earth's surface (Correct answer)
- To specify the map projection algorithm used
- To set the scale of the resulting map
Correct answer: To define the origin and orientation of the coordinate system relative to the Earth's surface
A datum defines the reference ellipsoid and its alignment to the Earth, anchoring the coordinate system so that coordinates correspond to real-world locations.
Question 2: Which file in an Esri Shapefile format stores the attribute data for features?
- .shp
- .shx
- .dbf (Correct answer)
- .prj
Correct answer: .dbf
The .dbf file is a dBASE-format table that stores non-spatial attribute data linked to each feature in the shapefile.
Question 3: In GIS analysis, what does 'attribute join' accomplish?
- Merges two layers based on their spatial overlap
- Links records from a table to features based on a shared key field (Correct answer)
- Reprojects a layer into a new coordinate system
- Converts point features into polygon features
Correct answer: Links records from a table to features based on a shared key field
An attribute join appends columns from an external table to a feature layer's attribute table using a common field (key) present in both.
Question 4: What problem does 'rubber sheeting' (spatial adjustment) correct in GIS?
- Incorrect attribute values in scanned map layers
- Geometric distortions in a dataset by stretching it to align with control points (Correct answer)
- Color inconsistencies between adjacent map tiles
- Projection mismatch between raster and vector layers
Correct answer: Geometric distortions in a dataset by stretching it to align with control points
Rubber sheeting warps a dataset non-uniformly by anchoring control points to correct positions, effectively stretching the layer like a rubber sheet to fit.
Question 5: Which format is specifically designed to efficiently serve large raster datasets over the web with built-in overviews and tiling?
- GeoTIFF
- Cloud-Optimized GeoTIFF (COG) (Correct answer)
- ASCII Grid (.asc)
- ERDAS Imagine (.img)
Correct answer: Cloud-Optimized GeoTIFF (COG)
A Cloud-Optimized GeoTIFF organizes internal tiles and overviews so web clients can request only the needed portion via HTTP range requests without downloading the whole file.
Question 6: What is 'data generalization' in cartography and GIS?
- Adding detailed attributes to feature records
- Simplifying or abstracting geographic features to suit a smaller map scale (Correct answer)
- Converting geographic coordinates to projected coordinates
- Merging duplicate records in an attribute table
Correct answer: Simplifying or abstracting geographic features to suit a smaller map scale
Generalization reduces detail (e.g., smoothing a coastline or merging small polygons) so features remain legible and meaningful at a smaller map scale.
Question 7: In the context of LiDAR point clouds, what does 'point density' measure?
- The vertical accuracy of each elevation return
- The number of laser returns per unit area, typically points per square meter (Correct answer)
- The wavelength of the laser used during acquisition
- The percentage of ground-classified points in the dataset
Correct answer: The number of laser returns per unit area, typically points per square meter
Point density (points/m²) indicates how closely spaced LiDAR returns are, directly affecting the level of surface detail that can be extracted.
GIS Geospatial Data Fundamentals 4
What is the purpose of a datum in a coordinate reference system?