Na+ or Ca2+ . Which ion has the larger radius?
The thing is that you need to know the coordination environment in the first place as ionic radii are C.N.-dependent. From Shannon's canonical paper "Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides"[1]: 

\begin{array}{cc}
\hline
\text{Ion} &amp; \text{C.N.} &amp; \text{C.R., Å} &amp; \text{I.R., Å} \\
\hline
\ce{Na+} &amp; 4 &amp; 1.13 &amp; 0.99 \\
&amp; 5 &amp; 1.14 &amp; 1.00 \\
&amp; 6 &amp; 1.16 &amp; 1.02 \\
&amp; 7 &amp; 1.26 &amp; 1.12 \\
&amp; 8 &amp; 1.32 &amp; 1.18 \\
&amp; 9 &amp; 1.38 &amp; 1.24 \\
&amp; 12 &amp; 1.53 &amp; 1.39 \\
\hline
\ce{Ca^2+} &amp; 6 &amp; 1.14 &amp; 1.00 \\
&amp; 7 &amp; 1.20 &amp; 1.06 \\
&amp; 8 &amp; 1.26 &amp; 1.12 \\
&amp; 9 &amp; 1.32 &amp; 1.18 \\
&amp; 10 &amp; 1.37 &amp; 1.23 \\
&amp; 12 &amp; 1.48 &amp; 1.34 \\
\hline
\end{array}

where C.N. - coordination number; C.R. - crystal radius; I.R. - ionic radius. The data is also available online for free. Comparing similar coordination environments, it's easier to notice that overall $\ce{Na+}$ is indeed larger than $\ce{Ca^2+}$:



Reference


Shannon, R. D. Acta Cryst A, 1976, 32 (5), 751–767 DOI: 10.1107/S0567739476001551.