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Proxy data reflecting the oxygen isotope composition of meteoric precipitation (δ¹⁸O_ppt) 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 δ¹⁸O_ppt 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 δ¹⁸O_ppt compositions based on latitude and altitude. Model value and residual grids are combined to derive a high-resolution global map of δ¹⁸O_ppt that can serve as a spatial reference against which proxy data for …