18-Geom-A7 Geospatial Information Systems · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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 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 datum is the reference framework that fixes the origin, orientation and scale used to express positions, so that coordinates have a defined physical meaning. A horizontal (geodetic) datum pairs a reference ellipsoid with a set of station coordinates (a realization) that anchors it to the Earth, allowing latitude and longitude to be defined; a vertical datum defines the zero surface (typically the geoid/mean sea level) from which heights are measured. In a GIS the datum matters critically because every layer must be referred to the same datum before overlay — mixing datums can shift features by tens or even hundreds of metres. Three commonly used examples: NAD83(CSRS), the North American Datum of 1983 in its Canadian Spatial Reference System realization (the current standard horizontal datum in Canada); WGS84, the global datum used by GPS/GNSS; and NAD27, the older North American Datum still found in legacy maps and datasets. For heights, CGVD2013 is Canada's current vertical datum, replacing CGVD28. Because these datums differ, a GIS must apply a datum transformation (not just a projection change) when integrating data referenced to different datums.
