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18-Geom-A7 Geospatial Information Systems · May 2014

Question 7 of 23: Vector and Raster Data Models

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams — May 2014 — 04-Geom-A7 Geospatial Information Systems. Closed-book; no calculator permitted. Format: twenty-three short-answer questions of equal value (5 marks each); a candidate answers any twenty, but all twenty-three are solved in full below. Datum and coordinate conventions follow the Canadian spatial reference framework — NAD83(CSRS) horizontally and CGVD2013 vertically.

Reference texts: P. A. Longley, M. F. Goodchild, D. J. Maguire & D. W. Rhind, Geographic Information Systems and Science (4th ed., Wiley, 2015); P. Bolstad, GIS Fundamentals: A First Text on Geographic Information Systems (6th ed., XanEdu, 2019); P. A. Burrough, R. A. McDonnell & C. D. Lloyd, Principles of Geographical Information Systems (3rd ed., Oxford, 2015); M. Worboys & M. Duckham, GIS: A Computing Perspective (2nd ed., CRC, 2004); ISO 19115 Geographic information — Metadata.

Question 7: Vector and Raster Data Models (5 marks)

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 vector model represents discrete features by their geometry, built from three primitives: points (single coordinate pairs, e.g., a well), lines/arcs (ordered strings of coordinates between nodes, e.g., a road) and polygons (closed rings bounding an area, e.g., a parcel). In a topological vector model these are organized as nodes, arcs and faces with explicit connectivity, and each feature carries a unique ID linking it to an attribute table. The raster model represents space as a regular grid (matrix) of cells (pixels); each cell holds one value, and location is implicit from the row/column index together with the grid origin and cell size. Its components are therefore the cell array, the cell (pixel) values, the resolution/cell size, and the georeferencing origin.

VectorRasterpolygon (nodes + arcs)
Figure — The same area feature stored as a vector polygon (exact boundary from nodes and arcs) and as a raster grid (the feature approximated by cells; boundary quality set by cell size).

Vector advantages: compact storage for discrete features, precise geometry and boundaries, explicit topology enabling network and adjacency analysis, and easy linkage of rich attributes. Vector disadvantages: more complex data structure, computationally heavier overlay, and poor representation of continuously varying surfaces. Raster advantages: simple, regular structure, ideal for continuous phenomena (elevation, temperature) and fast map-algebra/overlay, and a natural fit for remote-sensing imagery. Raster disadvantages: large storage (every cell stored), resolution-limited precision with blocky boundaries, and no inherent topology or discrete-object identity.