CH Geographic Information Systems 2 — Questions and Answers
Question 1: In GIS, what does a topology rule enforce when two polygon layers share a boundary?
- Shared edges must be exactly coincident with no gaps or overlaps (Correct answer)
- Each polygon must have a unique attribute value
- Polygon vertices must align to a 1-meter grid
- Adjacent polygons must have different fill colors
Correct answer: Shared edges must be exactly coincident with no gaps or overlaps
Topological integrity requires that shared edges between adjacent polygons are perfectly coincident, preventing gaps and overlaps that would cause spatial analysis errors.
Question 2: Which spatial reference system is most commonly used for global marine navigation data in hydrographic GIS applications?
- NAD83
- WGS84 (Correct answer)
- ED50
- GDA2020
Correct answer: WGS84
WGS84 is the standard geodetic datum used globally for GPS and marine navigation, making it the default for hydrographic GIS datasets.
Question 3: A hydrographer needs to convert bathymetric depth soundings from a local tidal datum to a geodetic ellipsoidal height. Which tool is essential for this conversion?
- A vertical datum transformation model such as VDatum (Correct answer)
- A horizontal reprojection algorithm
- A raster resampling filter
- A topological validation engine
Correct answer: A vertical datum transformation model such as VDatum
VDatum (or equivalent vertical datum transformation models) converts between tidal datums, geoids, and ellipsoids, which is critical for integrating bathymetric data into geodetically referenced GIS.
Question 4: What is the primary purpose of a spatial index in a GIS database?
- To define the coordinate system of a layer
- To speed up spatial queries by organizing features by location (Correct answer)
- To enforce attribute data types
- To compress raster datasets
Correct answer: To speed up spatial queries by organizing features by location
Spatial indexes (such as R-tree or quadtree structures) organize features by geographic location so the database can rapidly identify candidates for spatial queries without scanning every record.
Question 5: In a hydrographic GIS workflow, which interpolation method is best suited for generating a smooth bathymetric surface from irregularly spaced soundings while honoring all input data points?
- Inverse Distance Weighting (IDW)
- Kriging
- Natural Neighbor
- Triangulated Irregular Network (TIN) (Correct answer)
Correct answer: Triangulated Irregular Network (TIN)
A TIN connects soundings with triangular facets and passes exactly through all input points, making it ideal for bathymetric surfaces where exact depth values must be preserved.
Question 6: Which GIS data format is the IHO standard for the exchange of digital hydrographic data?
- Shapefile (.shp)
- S-57 (.000) (Correct answer)
- GeoJSON
- KML
Correct answer: S-57 (.000)
IHO S-57 is the international standard transfer format for digital hydrographic data used in Electronic Navigational Charts (ENCs).
Question 7: When performing a buffer analysis around a charted hazard in a GIS, which parameter determines the zone of influence around the feature?
- The feature's attribute table field count
- The buffer distance and units (Correct answer)
- The layer's coordinate system name
- The raster cell size of the background layer
Correct answer: The buffer distance and units
The buffer distance (and its measurement units) defines the radius of the zone created around a hazard feature, which is the critical parameter controlling the output geometry.
CH Geographic Information Systems 2
In GIS, what does a topology rule enforce when two polygon layers share a boundary?