The Coulomb phase of a quantum field theory, when present, illuminates the analysis of its line operators and one-form symmetries. For 4d N = 2 field theories the low energy physics of this phase is encoded in the special Kähler geometry of the moduli space of Coulomb vacua. We clarify how the information on the allowed line operator charges and one-form symmetries is encoded in the special Kähler structure. We point out the important difference between the lattice of charged states and the homology lattice of the abelian variety fibered over the moduli space, which, when principally polarized, is naturally identified with a choice of the lattice of mutually local line operators. This observation illuminates how the distinct S-duality orbits of global forms of N = 4 theories are encoded geometrically. Contents 1 Introduction 1 2 Charge lattices in 4d QFTs 5 3 Non-principal Dirac pairings for N =4 super Yang-Mills 8 4 Comparison to CB geometry constructions 11 4.1 Review of N = 4 moduli space geometry 12 4.2 Connection between special Kähler structures and Dirac pairing 13 4.3 N =2 * Coulomb branch geometries 16 4.4 Other curves for su(2) and su(3) N =4 sYM 18 A Properties of simple Lie algebras and groups 20 B Invariant factors of a symplectic form 22 C Maximal symplectic sublattices of Λ J 24