In Mwotlap, an Oceanic language of Vanuatu, the principal device for referring to space is a paradigm of six directionals. Organized in pairs, these morphemes define three ways to draw a vector in space: by reference to a salient participant (hither-thither); by reference to an asymmetry perceptible within the immediate, local setting (up-down; in-out); or by reference to a fixed, absolute system of four horizontal quadrants (also lexified as up-down; in-out). These three "coordinate sets" can be shown to obey a strict hierarchy, determining which one the speaker should activate in a given situation. After providing an overview of this directional system, this paper investigates in more detail the mechanics of geocentric reference in Mwotlap, whereby a land/sea axis (inout) is crossed by a second axis, running from [south]east (up) to [north]west (down). In order to account for this use of the vertical directionals up-down on the horizontal plane, a semantic hypothesis is proposed that is related to the seafaring history of Mwotlap's population.