Proxy data reflecting the oxygen isotope composition of meteoric precipitation (δ18Oppt) are widely used in reconstructions of continental paleoclimate and paleohydrology. However, actual geographic variation in modern water compositions is difficult to estimate from often sparse data. A first step toward understanding the geologic pattern of change in δ18Oppt is to describe the modern distribution in terms of principal geographic parameters. To this end, we empirically model relationships between 18O in modern precipitation and latitude and altitude. We then identify geographic areas where large-scale vapor transport patterns give rise to significant deviations from model δ18Oppt compositions based on latitude and altitude. Model value and residual grids are combined to derive a high-resolution global map of δ18Oppt that can serve as a spatial reference against which proxy data for paleoprecipitation can be compared. Reiteration of the procedure outlined here, for paleo-δ18Oppt data, may illuminate past changes in the climatic and physiographic parameters controlling the distribution of δ18O regimes.