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18-Geom-A7 Geospatial Information Systems · May 2017

Question 4 of 15: Site-selection flowchart (school siting)

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

Notes on this paper

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 4: Site-selection flowchart (school siting) (10 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.

Given. Three input layers — a road map, a stream map and a land-use layer. Constraints: a candidate site must be > 300 m from major roads and > 500 m from streams, and must fall on a suitable land-use class. Find. A flowchart of the input layers, processing (geoprocessing) functions and the output that solves the siting problem.

Approach. This is a classic constraint-overlay (Boolean suitability) model: buffer each exclusion feature by its distance, combine and invert the buffers to obtain the permitted area, then overlay that with the suitable land use to obtain candidate sites.

Road map (input layer) Stream map (input layer) Land-use data (input layer) Buffer roads 300 m Buffer streams 500 m Select suitable land-use classes Union (merge) road + stream buffers Erase restricted zone from study area Permitted area (outside both buffers) Suitable land-use areas Intersect / overlay permitted ∩ suitable Candidate school sites (output map)
Figure — constraint-overlay model. Input layers (light) feed geoprocessing functions (blue) that buffer, combine and invert the exclusion zones, then overlay the permitted area with suitable land use to yield the candidate-site output (green).
  1. Buffer the exclusion features. Buffer the road map by 300 m and the stream map by 500 m, producing two "too-close" zones.
  2. Combine the buffers. Union (merge) the road and stream buffers into a single restricted zone that violates either constraint.
  3. Invert to the permitted area. Erase the restricted zone from the study-area extent (a complement/NOT operation), leaving only land that is beyond 300 m of roads and beyond 500 m of streams.
  4. Reclassify land use. Select (reclassify) the land-use layer to the classes acceptable for a school, giving the suitable-land polygons.
  5. Overlay for candidates. Intersect the permitted area with the suitable-land polygons; the result is the map of candidate school sites that satisfy every constraint.