Superlative descriptions like to be limited to a particular groups of things to be compared. People are best in their class, a mountain might be the tallest in the lower 48 states, and several things are no doubt the best inventions since sliced bread. Of course, something could always just be the worst idea ever. One way to express how you’re limited the domain of compared items is to use the phrase this side of X. Now, you can’t go around using this for just any sort of domain limitation. It works really well when you’re talking about geographically limiting the domain of comparison to…well, shouldn’t it be obvious? Here’s some old timey examples from the OED.
1840 T. C. HALIBURTON Clockmaker III. xviii, He is..the best live one that ever cut dirt this side of the big pond.
1914 Sat. Even. Post 4 Apr. 10/2 There ain’t a kid like him this side of the Hump [sc. mountain range in west of N. America]–nor t’other side either.
Big, or at least salient, geographic features seem to work well – oceans, mountain ranges, mason-dixon lines. Also good are salient locations. Nearby pizza favorite Zachary’s has been lauded as the best pizza this side of Chicago. A place at Tahoe seems to have the best mesquite tri-tip and ribs this side of Texas. Now, it’s not clear to me that these claims are about, for example, taking the area between Chicago and the SF Bay Area and saying that there’s no better pizza in that region. It’s rather that they’re picking a place famous for pizza (or ribs), and saying that their own pizza may not be quite as good (or authentic), but it’s pretty darned close.