**9.4.2 Distance between Two Points along a Parallel of Latitude**

**1.**To find the distance along a parallel of latitude:

Distance between points
P and Q
= ( different in longitude in minutes ) x cos
latitude
=
(
θ x 60 x cos x^{o}
) nautical miles |

**Example:**

In the diagram above, calculate

(a) The distance of

*PQ*, measured along the parallel of latitude 34^{o}N,
(b) The distance of

*DM*, measured along the parallel of latitude 54^{o}S.

*Solution:***(a)**

Difference in longitude between

*P*and*Q*
= 40

^{o }+ 58^{o }= 98^{o}
Hence, the distance of

*PQ*, measured along the parallel of latitude 34^{o}N
= 98 x 60 x cos 34

^{o}← [θ x 60 x cos (latitude)]
=

**4874.74 n.m.**

**(b)**

Difference in longitude between

*D*and*M*
= 82

^{o }– 40^{o }= 42^{o}
Hence, the distance of

*DM*, measured along the parallel of latitude 54^{o}S
= 42 x 60 x cos 54

^{o}← [θ x 60 x cos (latitude)]
=

**1481.22 n.m.**