18-Geom-A7 Geospatial Information Systems · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2015 — 04-Geom-A7 Geospatial Information Systems. Closed-book; an approved Casio or Sharp calculator is permitted. Format: twelve short-answer questions of varying value totalling 100 marks; all questions constitute a complete exam and 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); J. P. Snyder, Map Projections — A Working Manual (USGS PP 1395); 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) Entity. An entity is a real-world phenomenon of interest that is represented in the GIS as a single, individually identifiable object — for example a specific parcel, road segment, well or lake. It is the "thing" being modelled, distinct from its computer representation (its geometry) and from its descriptors; in data-modelling terms it is the object about which spatial and attribute information is collected. (b) Attribute. An attribute is a named descriptive property of an entity — a characteristic recorded in a table column, one value per feature, such as a parcel's zoning, a road's surface type or a well's yield. Attributes answer what a feature is, as opposed to the geometry, which answers where it is. (c) Precision. Precision is the repeatability or exactness of a measurement or the level of detail to which a value is recorded (e.g., coordinates to the nearest millimetre) — how closely repeated observations agree with one another, independent of whether they are correct. (d) Accuracy. Accuracy is the closeness of a measured or recorded value to its true value; positional accuracy is commonly expressed as an RMSE relative to a higher-order reference. A dataset can be precise (tightly clustered, many decimals) yet inaccurate (biased away from the truth), so the two must be reported separately. (e) Topology. Topology is the explicit encoding of the spatial relationships between features — connectivity, adjacency and containment — that remain invariant under stretching, independent of exact coordinates. It lets a GIS know that two arcs share a node, that two polygons share a boundary, or that a point lies inside a polygon, and it is what enables network tracing, polygon overlay and error checking.
