What is half of the smallest unit of geometry measurement?

yocktometer = 10^-24 m

* * * * *

Not quite.

Firstly, it is yoctometre (without the k).

Second, 0.5 yoctometre would be half of this unit.

But most important, why stop at yocto?

You could carry on until at least the Planck length which is 1.616*10-35 metres.