Hello!
I’m following a course on geometry nodes, and at some point it is mentioned that the lenght of a normal is 1.
But how does that translate in a 3d scene with metric units? 1 meter, 10 centimeters, or something else?
Unit type is irrelevant. A normal is a vector that describes a direction not a distance.
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I guess, it just means “1 unit [of your choise]”.
If Scene Properties > Units set to “Metric” with scale of “1” (as per default settings, afaik), then it means “1 meter”.
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This is because a normal is a “normalized” vector, its magnitude (length) is not important, the important thing is its direction.
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it’s what is known as a unit vector:
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A vector consists of two things. A direction and a magnitude. Both are important. There are calculations when you will need the one or the other, or both. The magnitude is also called length but its just a scalar. There are unitvectors, but that refers to their length being 1 they are normalized. And 1 is their UNITLENGTH. They dont HAVE a unit like meters, as it about their numerical value, thats what gives it certain mathematical properties. You cant convert it into another lenth-unit and hope for it to behave the same.You should rather think of them as being a separate mathematical entiy.
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I’ll have to let the information sink in a little, but I think I understand. Thank you very much for your answers everyone!
Hello!
You can always do the science to find out:
As you can see, even though the unit measurement is set to Imperial Feet, internally Blender uses the Meter as its unit of measurement.
So, even though your choice of unit for a unit vector is arbitrary and just needs to remain consistent, for Blender the answer is 1 meter.
Hope that helps.
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I tried to replicate your example with a sphere with a radius of 5m, and normalizing it does indeed limit it at 1m. So thank you for the additional explanation!
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And a starting position 
In the case of normal’s the 2 important things are the start position and the direction, the magnitude can be infinite which is why they normalize it.
Sorry, that’s not right… Debuk is correct. Magnitude and Direction is all that is required for Vectors (see Wikipedia article).
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Well just with the help of a friend. In principle all vectors are located at the origin. Thats how it is. Its just three values in R^3. But you can use another vector to translate it or you could even simply imagine him to be anywhere like on the center of your face. But in reality he’s still at the origin. He’s just not utilizing the facepos in the normalcase, its not needed and for usage in blender much more practical to display them on the face. 
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