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18-Geom-A7 Geospatial Information Systems · December 2018

Question 12 of 15: Site-suitability model for a ski resort (flowchart)

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

Notes on this paper

Paper format. National Exams, December 2018 — 04-Geom-A7, Geospatial Information Systems. Closed book (one approved Casio or Sharp calculator permitted); duration 3 hours. Fifteen (15) questions are provided and any ten (10) constitute a complete paper; each question is of equal value (10 marks), so a complete paper totals 100 marks. Most answers are essay-format; clarity and organization count. All fifteen questions are solved below for completeness.

Reference texts (subject)

Longley, Goodchild, Maguire & Rhind, Geographic Information Systems and Science (4th ed.); P. Bolstad, GIS Fundamentals (5th ed.); Worboys & Duckham, GIS: A Computing Perspective (2nd ed.); Burrough, McDonnell & Lloyd, Principles of Geographical Information Systems (3rd ed.); de Smith, Goodchild & Longley, Geospatial Analysis; OGC Simple Feature Access (ISO 19125); ISO 19157 Geographic information — Data quality; ISO 19115 Metadata.

Question 12: Site-suitability model for a ski resort (flowchart) (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.

Approach. This is a constraint / weighted-overlay suitability model. Each of the four criteria maps to a standard geoprocessing function: proximity criteria become buffers, the slope criterion is derived from the DEM and reclassified, and the criteria are then combined by overlay (intersect the "must-have" zones, erase the "must-not" zones).

Road map (input layer) Stream map (input layer) Land-use data (agriculture) DEM (elevation) Buffer roads 500 m (keep INSIDE) Buffer streams 50 m (exclusion) Select agriculture, buffer 50 m (excl.) Slope from DEM Reclassify ≥ 35% Union exclusion zones (streams ∪ agriculture) Intersect: within 500 m of roads ∩ slope ≥ 35% (both required) Erase exclusion zone (remove too-close areas) Candidate ski-resort sites (output suitability map)
Figure — constraint-overlay flowchart. Input layers (light) feed geoprocessing functions (blue); "must-have" zones are intersected and "must-not" zones erased to yield the candidate-site output (green).
  1. Buffer roads (must-have proximity). Buffer the road map by 500 m; the inside of this buffer is the "within 500 m of major roads" zone.
  2. Buffer streams (must-not proximity). Buffer the stream map by 50 m to make the stream-exclusion zone.
  3. Select and buffer agriculture (must-not). Extract agricultural parcels from the land-use layer and buffer them by 50 m to make the agriculture-exclusion zone.
  4. Derive slope and reclassify (must-have). Compute slope (%) from the DEM and reclassify to keep only cells with slope ≥ 35 %.
  5. Union the exclusions. Merge the stream and agriculture buffers into a single restricted zone.
  6. Intersect the must-haves. Overlay (intersect) the within-500 m-of-roads zone with the ≥ 35 % slope area — land satisfying both positive criteria.
  7. Erase the restricted zone. Erase the unioned exclusion zone from the result of step 6, removing everything too close to streams or agriculture.
  8. Output. The remaining polygons are the candidate ski-resort sites that meet all four constraints.