To find the area by the grid square method: The grid square on toposheet measures 2 cm × 2 cm., or 1 km., × 1 km., since 2 cm., is equal to 1 km. Therefore, the area of each square is 1 sq. km. To find particular area on a topographical map: Note the number of complete grid square within the area and the number of squares lying within the area are not complete. (i) Square covered half are taken as 1 /2 squares. (ii) Square covered more than half are taken as 2/3 squares. (iii) Square covered less than half are taken as 1/3 squares. Add all the squares thus, the area which has to be found out is calculated.