Compute the actual area of plot in hectares:

A survey map is required to be drawn to a scale of 1/10000. A 30 m chain was used which was found to be accurate at commencement of work while 20 cm too long at the closure. The field of plot surveyed was found to be 80 cm² on map. Compute the actual area of plot in hectares.

Solution

Length of chain at commencement = 30.00 m

Length of chain at closure = 30.20 m

Length of chain during survey = 30.00 + 30.20/2 = 30.10 m

Area of plot surveyed as measured on map = 80 cm²

Area of plot surveyed as measured on ground = 80 × 10⁴ × 10⁴ cm²

= 80 × 10⁴ m2 = 80 ha.

True plot area on ground = (30.10/30.00)²× 80 = 80.5344 ha.