Area Measurements

Area from a map

1- Dividing the Area Into Regular and Irregular Shapes

Measure the dimension of each area Calculate the area of each part Calculate the sum of the regular and irregular areas Convert the map area to a ground area Example Total map area= 70+30+100+….=1500 cm2 Scale=1/2000 Ground area= (1500x2000x2000)/ 100x100 = 600000 m2

2- Graph Paper Method Plot the area on a graph paper Count the number of sq cm and sq mm Convert the map area to a ground area using the known scale

3- The Planimeter Method Mechanical planimeter Digital planimeter

tracing needle fixed block

Calibrate the planimeter before using it Make reading around a known area Example: reading around a 10x10 cm square area = 0.995 rev Reading around the required area = 5.765 rev Scale of the map =1/5000 Calculate the ground area

Area from ground measurements

1- Use the field measurements

Area A1 S= half the circumference of the triangle S=(50+40+80)/2 = 85 A1= A1= 818.15 m2 Total area= A1+A2+ irregular area

Area is produced directly in m2

Irregular Area

Irregular Area Simpson’s rule for curved boundaries The line joining three offsets is assumed as a parabola parabola h1 h2 h3 d d

2- Area from corner coordinates 2 (x2,y2) 1(x1,y1) 3(x3,y3)

Notes Points should be numbered in clockwise direction Divide the result by 2 to obtain the area

Area of circular segment