Forest Surveying, Mapping and GIS/Remote Sensing
Forest Surveying, Mapping and GIS/Remote Sensing tests measurement of land, map reading, spatial data models and image interpretation. Forestry officers use these skills for boundary surveys, inventory plots and change detection.
Core rules and concepts
- Surveying: chain or tape for distance, compass for bearing, level for elevation, theodolite and total station for angles and coordinates; GPS for positioning.
- Scale: 1:25,000 means 1 cm on the map equals 25,000 cm, or 250 m, on the ground. Area scale is the square of the linear scale.
- Contours join points of equal elevation; close contours mean steep slope; spacing indicates gradient.
- GIS: vector data as point, line and polygon; raster data as grid cells; attributes describe features; overlay, buffer and clip are common analyses.
- Remote sensing: spatial, spectral, temporal and radiometric resolution; NDVI = (NIR minus Red) divided by (NIR plus Red); accuracy assessment is essential.
- Nepal uses the Everest datum and UTM zones 44 and 45; the Survey Department produces topographic maps.
Worked example
On a 1:50,000 map, a boundary measures 4 cm. Ground distance = 4 x 50,000 cm = 200,000 cm = 2 km. A rectangular plot measures 2 cm by 3 cm on the map: each square centimetre represents 0.25 square kilometres, so the area is 6 x 0.25 = 1.5 square kilometres. The reasoning: convert map distance to ground distance by multiplying by the scale denominator, then square the linear conversion for area.
Traps
Do not multiply by the scale denominator and forget to convert centimetres to metres. Do not use the linear scale for area. Do not mix datums or UTM zones. Do not treat a classified satellite image as ground truth; it needs accuracy assessment.