Using latitude is a fundamental step in calculating the distance between two geographical locations, particularly for distances measured directly north or south along a line of longitude. The core idea is to determine the difference in latitude between the two points.
Understanding Latitude and Distance
Latitude lines run east-west and measure the distance north or south of the Earth's Equator. A degree of latitude represents an approximately constant distance on the Earth's surface because lines of longitude (meridians) are farthest apart at the Equator and converge at the poles, while parallels of latitude are roughly parallel.
Specifically, one degree of latitude is approximately equal to:
- 60 nautical miles
- 69 miles
- 111 kilometers
This consistent relationship makes calculating north-south distance relatively straightforward once the latitude difference is known.
Calculating the Difference in Latitude
To find the distance between two points using latitude, you first need to calculate the difference between their latitudes. The method depends on whether the points are in the same hemisphere (North or South) or different hemispheres.
Points in the Same Hemisphere
If both points are located in the Northern Hemisphere or both are in the Southern Hemisphere, you find the difference in latitude by subtracting the smaller latitude value from the larger one.
- Reference Information: As stated in the provided reference: "If both points are in the same hemisphere. Then the latitudes must be subtracted to obtain the difference in latitude. In this example both points are in the northern. Hemisphere."
For example:
- Point A: 40° N Latitude
- Point B: 35° N Latitude
- Difference in Latitude: 40° - 35° = 5°
Points in Different Hemispheres
If one point is in the Northern Hemisphere and the other is in the Southern Hemisphere, you find the difference in latitude by adding their absolute latitude values.
For example:
- Point C: 20° N Latitude
- Point D: 15° S Latitude
- Difference in Latitude: 20° + 15° = 35°
Converting Latitude Difference to Distance
Once you have the difference in latitude (in degrees), you can convert it into an approximate distance along a meridian (a north-south line) using the conversion factors mentioned earlier.
Formula (for distance along a meridian):
Distance ≈ (Difference in Latitude in Degrees) × (Distance per Degree of Latitude)
Examples:
- Using the first example (5° difference):
- Distance ≈ 5° × 60 nautical miles/° = 300 nautical miles
- Distance ≈ 5° × 111 km/° = 555 km
- Using the second example (35° difference):
- Distance ≈ 35° × 60 nautical miles/° = 2100 nautical miles
- Distance ≈ 35° × 111 km/° = 3885 km
| Latitude Difference (Degrees) | Approximate Nautical Miles | Approximate Kilometers |
|---|---|---|
| 1 | 60 | 111 |
| 5 | 300 | 555 |
| 10 | 600 | 1110 |
| 35 | 2100 | 3885 |
This method provides the distance measured directly north or south. For calculating the shortest distance between two points that are not on the same meridian (i.e., they also have different longitudes), more complex formulas like the Haversine formula are used, which account for the Earth's curvature and both latitude and longitude differences. However, the difference in latitude remains a key component, especially for calculating the north-south component of the distance.
