What is a False Northing or False Easting?


In land surveying/GIS etc. I hear this term False Northing or False Easting. What does it mean?

In: Mathematics

Here’s a practical example: suppose we take a map and make a vertical line through the center of it. This is our meridian. Now, let’s divide the remaining halves into 4, leaving us with 8 equal strips consisting of 9 equidistant lines. The edges will also count as lines. Don’t run into the [fence post](https://en.wikipedia.org/wiki/Off-by-one_error#Fencepost_error)!

Now, we want to specify which line we’re on, so let’s number each line. We could start by calling the meridian “0”. The line to the west would be “–1” and the line to the east would be “+1”. However, negative numbers can be tricky to work with and might be misread. A bit of smudged ink might literally put you on the other side of the planet! Instead, we could just number them 1 to 9. In doing this, we’ve created a *false easting* of 5!

Subtracting the false easting from a given number will give you the true easting. If you subtract 5 from 5, you get zero, so you know that the 5th line in sequence is the meridian of this map. Subtracting 5 from the easternmost edge would give you 4. Subtracting 5 from the westernmost edge would give you –4.

It’s a trifle more complicated than that, but not by much. This isn’t the *only* use for a false easting or northing, but it’s a common one. Some projections have standardized false eastings. For example, the UTM projection uses a false easting of 500,000 meters for each zone.

False northings are the same—just in a different direction.