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.
(a) Object-oriented vs relational data model. The relational model stores data as flat two-dimensional tables (relations) of rows and columns, related to one another through shared key values and manipulated by relational algebra / SQL. It is mature, standardized, transaction-safe (ACID) and simple, but complex geographic objects sit awkwardly in flat tables — historically geometry was pushed into an opaque BLOB or a separate coordinate table. The object-oriented model stores data as objects that encapsulate both state (attributes and geometry) and behaviour (methods), organized into class hierarchies with inheritance, encapsulation and polymorphism. It represents complex, nested or topological features and their operations naturally (a Parcel object that knows how to compute its own area, a subtype hierarchy of geometry classes as in Q15). The dominant compromise in practice is the object-relational database (PostGIS, Oracle Spatial): relational tables extended with rich geometry types and spatial methods — keeping SQL and ACID while gaining object-like geometry behaviour. In short: relational = tables + keys + SQL (simple, standard, weak on complex objects); OO = objects + inheritance + methods (rich modelling, less standardized); object-relational blends the two.
(b) Spatial functions vs spatial constraints. Spatial functions are operations that compute or derive spatial results from existing data — buffer, intersect, union, distance, area, centroid, spatial join, overlay. They do something and return new geometry or values; they are how analysis is performed. Spatial constraints are rules that restrict what spatial configurations are valid — integrity conditions the data must satisfy: parcels must not overlap, a parcel must tile without gaps, a building must lie within a parcel, road segments must connect at shared nodes, a geometry must be simple (non-self-intersecting). They do not transform data; they enforce validity and are checked when data are edited or loaded (often as topology rules). Put simply, functions produce spatial answers, while constraints guard spatial correctness — one is active analysis, the other is passive integrity.
