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18-Geom-A7 Geospatial Information Systems · May 2014

Question 12 of 23: Buffers in Proximity Analysis

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

Notes on this paper

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 12: Buffers in Proximity Analysis (5 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.

A buffer is a new polygon that encloses all the area within a specified distance of a feature — a point, line or polygon. Proximity analysis uses buffers to answer "what is near?" questions by making nearness into an explicit, mappable zone that can then be combined with other layers. The workflow is: generate a buffer at the chosen distance (which can be a fixed distance or vary by an attribute, e.g., wider buffers for busier roads), then overlay that buffer with other layers to select, count or measure the features and area that fall inside it.

pointpoint buffer (radius d)line buffer (corridor ±d)
Figure — A buffer converts "within distance d" into an explicit zone; overlaying it with other layers selects everything inside.

Typical GIS applications: delineating a riparian setback (e.g., a 30 m buffer along a stream) and finding land parcels that intersect it; noise or safety zones around a highway or pipeline; service areas around facilities (which parcels lie within 500 m of a fire hall); and site-selection constraints (exclude everything within a buffer of wetlands or wells). By turning distance into geometry, buffering lets the GIS use standard overlay and query to identify, measure and report everything within the proximity zone.