CH Geographic Information Systems 4

Question 1

In raster GIS, what does 'resampling' refer to when changing the cell size of a bathymetric grid?

Accepted Answer

Recalculating cell values when converting between grid resolutions using methods like nearest neighbor or bilinear interpolation

Answer

Resampling recalculates cell values when a raster is reprojected or rescaled, using algorithms like nearest neighbor, bilinear, or cubic convolution to estimate new cell values.

Question 2

What is the purpose of the S-57 Object Catalog in hydrographic GIS?

Accepted Answer

It defines all permissible object classes, attributes, and their relationships for ENC data

Answer

The S-57 Object Catalog (IHO Publication S-57 Appendix A) defines the complete dictionary of feature classes and attributes allowed in Electronic Navigational Charts.

Question 3

Which attribute of a GIS point feature is most critical for validating the absolute horizontal accuracy of a sounding position?

Accepted Answer

The horizontal uncertainty value associated with each position

Answer

The horizontal uncertainty (or positional accuracy) attribute quantifies the confidence in each sounding's geographic position, which is essential for IHO Order compliance.

Question 4

When overlaying two polygon layers in GIS, which operation retains only the area that exists in BOTH input layers?

Accepted Answer

Intersect

Answer

The Intersect operation outputs only the geographic area and attributes common to both input polygon layers, discarding everything outside the overlap.

Question 5

A GIS layer for charted obstructions uses the IHO object class 'OBSTRN'. Which attribute would indicate whether the obstruction is a wreck, rock, or submerged pile?

Accepted Answer

CATOBS (Category of Obstruction)

Answer

CATOBS is the S-57 attribute that categorizes the type of obstruction (e.g., wreck, rock, submerged pile), distinguishing between different hazard types under the OBSTRN object class.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Geographic Information Systems 4