How do I calculate in meters how far away I am with Latitude and longitude?

Question

To make it clearer, if I was given a longitude of 41 what would be the formula? How would I work out how far I am from the Prime meridian, along the surface of the earth, in meters?

And likewise if I was given a latitude of say -61 how would I work out how far I am from the equator?

Answer 1

At the equator or along a meridian, one degree corresponds to roughly 111 km, or one arc-minute corresponds quite well to one nautical mile (1852 m). Even these simple approximations are not 100% correct, e.g., because the earth is not a perfect sphere; but I bet they are good enough for your application.

For two points that are away from the equator but in relatively short distance to each other, you may use the following as as simple approximation:

1. Compute the north-south distance as above, i.e., one nautical mile per arc-minute in latitude difference
2. For the west-east distance, calculate one nautical mile per arc-minute in longitude difference, but multiply the result with the sine of the common (almost identical) latitude.
3. Use pythagoras to compute the "diagonal" distance from the north-south and west-east distance

Again, this approximation is not perfect, but certainly good enough for most everyday applications. In some cases, you may even want to let the elevation difference enter into the Pythagoras calculation ...