CH Geographic Information Systems 2

Question 1

In GIS, what does a topology rule enforce when two polygon layers share a boundary?

Accepted Answer

Shared edges must be exactly coincident with no gaps or overlaps

Answer

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?

Accepted Answer

WGS84

Answer

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?

Accepted Answer

A vertical datum transformation model such as VDatum

Answer

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?

Accepted Answer

To speed up spatial queries by organizing features by location

Answer

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?

Accepted Answer

Triangulated Irregular Network (TIN)

Answer

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.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Geographic Information Systems 2