18-Geom-A7 Geospatial Information Systems · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, December 2018 — 04-Geom-A7, Geospatial Information Systems. Closed book (one approved Casio or Sharp calculator permitted); duration 3 hours. Fifteen (15) questions are provided and any ten (10) constitute a complete paper; each question is of equal value (10 marks), so a complete paper totals 100 marks. Most answers are essay-format; clarity and organization count. All fifteen questions are solved below for completeness.
Longley, Goodchild, Maguire & Rhind, Geographic Information Systems and Science (4th ed.); P. Bolstad, GIS Fundamentals (5th ed.); Worboys & Duckham, GIS: A Computing Perspective (2nd ed.); Burrough, McDonnell & Lloyd, Principles of Geographical Information Systems (3rd ed.); de Smith, Goodchild & Longley, Geospatial Analysis; OGC Simple Feature Access (ISO 19125); ISO 19157 Geographic information — Data quality; ISO 19115 Metadata.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The three relationship types drawn with distinct notations in the diagram are generalization (hollow triangle), aggregation (hollow diamond) and composition (filled diamond); a plain line also links Geometry to Spatial Reference System as a simple association. They are illustrated below.
1) Generalization (inheritance), hollow triangle pointing to the superclass. This is an "is-a" relationship: a subclass inherits the attributes and operations of its superclass. In the schema, Point, LineString, Polygon and Geom_Collection are subclasses of the abstract Geometry; Line and LinearRing specialize LineString; and MultiPoint, MultiLineString and MultiPolygon specialize Geom_Collection. Its function is to share common structure and behaviour in one place and to enable polymorphism — any operation defined on Geometry (e.g., a spatial-reference-system reference, an envelope, an equals test) is automatically available to every geometry type.
2) Aggregation (weak whole–part), hollow diamond on the "whole". This is a "has-a" relationship in which the parts can exist independently of the whole. A LineString aggregates two-or-more (2..*) Points: the line is built from points, but a point is a self-standing object that does not depend on the line for its existence. Its function is to model containment/grouping without lifecycle dependency — parts may be shared or outlive the whole.
3) Composition (strong whole–part), filled diamond on the "whole". This is a stronger "has-a" in which the parts' existence is bound to the whole — the parts are owned exclusively and are created and destroyed with it. A Polygon is composed of one-or-more (1..*) LinearRings (its exterior and interior boundaries), and a MultiPolygon is composed of its member Polygons; these parts have no independent life outside their container. Its function is to express exclusive ownership and cascading lifecycle — deleting the whole deletes its parts.
The remaining plain line between Geometry and Spatial Reference System is a simple association — a general semantic reference stating that every geometry is defined in a spatial reference system — included here for completeness beyond the three whole-part/inheritance relationships the question asks about.
