  String and 5-brane junctions are shown to succinctly classify all known 8d
${\cal N}$=1 string vacua. This requires an extension of the description for
ordinary $[p,q]$-7-branes to consistently include O7$^+$-planes, which then
naturally encodes the dynamics of $\mathfrak{sp}_n$ gauge algebras, including
their higher-form center symmetries. Central to this analysis are loop
junctions, i.e., strings/5-branes which encircle stacks of 7-branes and
O7$^+$'s. Loop junctions further signal the appearance of affine symmetries of
emergent 9d descriptions at the 8d moduli space's boundaries. Such limits
reproduce all 9d string vacua, including the two disconnected rank (1,1) moduli
components.
