Weighing wind: a GIS overlay for a community wind farm
A regional development agency uses a GIS suitability model to choose between two sites for a three-turbine community wind farm. The model combines wind speed (40% weight), distance to the national grid (25%), land tenure (20%), and distance from residential areas (15%). Site A scores 82/100: mean wind speed 9.1 m/s, 3.2 km to grid, on private farmland, 1.8 km from the nearest dwelling. Site B scores 76/100: mean wind 8.2 m/s, 7.5 km to grid, on a conservation stewardship block, 2.4 km from dwellings. The overlay is a simple weighted sum with all criteria mapped at 1:50,000. The agency has a $12 million budget and must decide within eight weeks. Local iwi have requested that the cultural landscape values of the stewardship block be assessed, but no cultural criteria are in the model. A residents' group argues that the 1.8 km buffer at Site A is too small. The agency wants a defensible decision.
1. Explain how the choice of criteria, weights, and scale in the GIS model shapes the result. Identify one limitation of the weighted-sum approach in this case.
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The model is not neutral. Wind speed carries 40% of the weight, and Site A's higher wind (9.1 vs 8.2 m/s) gives it a large advantage; grid distance (25%) also favours A (3.2 vs 7.5 km), as does private farmland under the land-tenure criterion (20%). The residential buffer (15%) might favour B because 2.4 km is larger than 1.8 km, but it is the smallest weight. Because most criteria point to A, the output is likely predetermined unless weights are changed substantially. The 1:50,000 scale is too coarse for a 1.8 km buffer and may miss individual dwellings, cultural sites, or transmission constraints. A limitation of weighted-sum is that it assumes criteria are independent and fully compensable: a high wind score can offset cultural harm or residential amenity loss. That is a value judgement, not a technical one. The model also excludes cultural landscape values entirely, so it cannot represent mana whenua concerns; adding a criterion later would require re-running and re-weighting, which could change the ranking.
2. Evaluate the claim that Site A is the better option. Recommend a decision process, including how cultural values and uncertainty should be handled.
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Site A is better only on the model's chosen criteria. It has stronger wind, lower grid connection cost, and is on private land, which may simplify consenting. But 'better' depends on purpose: if the goal is least conflict and recognition of cultural values, Site B may be preferable despite lower output. The 1.8 km buffer is not automatically unsafe; the relevant standard depends on turbine size, noise, and shadow flicker. The $12m budget and eight-week deadline create pressure to accept the score. I would not treat 82 vs 76 as decisive because the difference is within plausible weight sensitivity. A defensible process would: (1) run a sensitivity analysis with alternative weights and a veto for cultural harm; (2) commission an iwi-led cultural landscape assessment before ranking; (3) verify dwelling locations and noise at 1:10,000 or by site survey; (4) compare energy yield and cost per kWh, not just score; (5) use a multi-criteria deliberative panel with iwi, residents, and technical experts. If the cultural assessment finds significant values at Site B, Site A may be the pragmatic choice, but only with robust conditions and community benefit sharing.