Spartina marshes (S. patens [Salt Meadow Cordgrass] and S. alterniflora [Saltmarsh Cordgrass]) are critical foraging, nursery, and overwintering habitats for Malaclemys terrapin (Diamondback Terrapin). However, the relationships between Spartina marsh quality, quantity, and distribution and resulting Diamondback Terrapin distribution, abundance, and movements are poorly understood. To develop a model for predicting these relationships, we needed a way to prioritize the locations where data are collected for model building. As an initial effort, we used available data on New York Spartina salt marsh distribution and estimates of Diamondback Terrapin home range to identify marshes for initial surveys and pilot work for studies of habitat quality. We present GIS-model results showing New York locations with 50-, 100-, and 260-ha hypothetical home ranges (consisting of 50%, 75%, and 100% Spartina marsh), and use this information to identify New York locations most likely to harbor Diamondback Terrapins. Our models indicated there should be relatively large populations of terrapins in western Hempstead Bay and eastern Jamaica Bay, but failed to identify a known terrapin population at Piermont Marsh on the Hudson River.