**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 ) × cos latitude
=
( θ × 60 × 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 × 60 × cos 34

^{o}← [θ × 60 × 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 × 60 × cos 54

^{o}← [θ × 60 × cos (latitude)]=

**1481.22 n.m.**