Measuring distance

Leon, you often say, “you always measure distances from Longitude scale” – I believe you mean Latitude?

 

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This is a very common question I get and does always result in some confusion. But as long as we do it correctly, that’s the most important thing!

Well, you actually do measure distance along a longitude!

A longitude is a vertical line going from pole to pole and a latitude is a line going from east to west. And if you wish to know how far north or south you are (i.e. on which latitude you are) you read this off the vertical line, which actually is a longitude. So to measure your latitude, you have to look along a longitude and if you wish to know how far you are to the east or west (i.e. which longitude you are on) you look along a line which is horizontal, i.e. a latitude.

When this makes sense, you need to know that you measure distances along a great circle on the globe. And where are great circles on the chart? The equator is one (and the only latitude around) and then we have all the longitudes going vertically from pole to pole in north-south direction. So it’s along a longitude you measure your distances.

The fact that you do not only measure distance but also read off your latitude along the same line is also true, of course.

But as I said, as long as we all agree that we measure distances along a vertical north-south going line on the chart, we are all agreeing. Whatever you want to call this line….