How do you arrange elements' ionic size?

The ionic radii is listed in $\text{pm} = {10}^{-} 12 \cdot m$; a measurement in $\text{Angstroms}$, ${10}^{-} 10 \cdot m$, is more useful for a chemist...... Anyway, for the metallic cations, we see that the ionic radii, the orange circles, are greatly reduced with respect to the parent atom. Why? Because we are removing valence electrons, whose radius defines the atomic radius. And upon their removal these radii becomes decidely smaller......
On the other hand, the situation is reversed for anions with repsect to their parent atoms. Because the anions are reduced, another electron(s) have been added to the valence shell. This expands the anionic radii because the nuclear charge is still the same and the valence shell expands to accommodate the extra electron(s).......The ionic radius of the nitride ion, $1.71$ $\stackrel{\circ}{A}$, versus the atomic radius of $0.70$ $\stackrel{\circ}{A}$, for the nitrogen atom is quite persuasive of this argument.