18-Geom-A7 Geospatial Information Systems · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2017 — 04-Geom-A7 Geospatial Information Systems. Closed-book; any non-communicating calculator permitted. Format: fifteen questions of varied value totalling 100 marks; fifteen questions constitute a complete paper and all fifteen are solved in full below. Most answers are required in essay form. 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); H. Samet, The Design and Analysis of Spatial Data Structures (Addison-Wesley, 1990); 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.
Georeferencing is the process of assigning real-world map coordinates (a defined coordinate reference system — datum and projection) to spatial data that initially have only an arbitrary internal coordinate system, such as a scanned paper map, an aerial photograph, a satellite image or a CAD drawing. It is typically done by identifying ground-control points of known coordinates and computing a transformation (affine, polynomial or, for elastic fits, rubber-sheeting) that warps the source into the target CRS, with residuals reported as an RMSE. Its purpose is to place every dataset into a common, real-world spatial framework so that layers register — line up correctly with one another and with the ground. This is the precondition for everything a GIS does: overlaying and integrating multiple layers, making accurate measurements of distance and area, performing spatial analysis and queries, and combining data from different sources, scales and epochs. Without georeferencing, an image or drawing would "float" with no true location, could not be overlaid on other data, and could not support measurement or analysis. In Canada the target framework is normally NAD83(CSRS) with a UTM or MTM projection.
