my($lat_key, $lon_key) = split(/./, $, 2);

In addition to hippo's comment, note that the quoted extract from this does not compile. While there is a $, Perl special variable (see perlvar), you don't seem to be using it (nor would I recommend doing so in this application). I suspect this is just a cut/paste error and not the error your code is actually producing, but again, who knows?

 Win8 Strawberry 5.8.9.5 (32) Mon 01/11/2021 18:12:15
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings

$, = 'foo.bar';
my($lat_key, $lon_key) = split(/\./, $, 2);
Number found where operator expected at - line 3, near "$, 2"
        (Missing operator before 2?)

^Z
syntax error at - line 3, near "$, 2"
Execution of - aborted due to compilation errors.
[download]