- 2081 Bhadra · 5 marks
Arithmetic mean, Thiessen, isohyetal methods compared
Short answer
Arithmetic mean ignores gauge location; Thiessen polygon assigns area weights to each gauge; isohyetal method uses isohyets and considers topography, best for hilly areas. Accuracy and effort increase in that order.
Differentiate Arithmetic Mean, Thiessen Polygon and Isohyetal Methods.
| Point | Arithmetic mean | Thiessen polygon | Isohyetal |
|---|---|---|---|
| Principle | Simple average of gauge values | Weighted average with weights equal to polygon areas | Weighted average using areas between isohyets |
| Formula | |||
| Map needed | No | Yes (polygons) | Yes (isohyets) |
| Gauge position | Ignored | Considered | Considered |
| Topography / orography | Ignored | Not considered | Considered |
| Suitable for | Flat area, uniform gauges | Plains, moderate relief, uneven gauges | Hilly/mountainous areas, large catchments |
| Accuracy | Lowest | Better | Highest |
| Effort | Very small | Moderate; redraw if gauge changes | Most; needs judgement and many gauges |
✓ Answer checked by Claude Sonnet 5.5
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