The goal of anywhere, anytime medical information exchange is impeded by the plethora of local conventions for identifying health data in separate electronic systems. Clinicians, administrators, and researchers all need a complete set of clinical information, coalesced from all of the various sources that produce health data. Mapping local terms to a standardized vocabulary such as LOINC bridges the many islands of health data that exists and facilitates data aggregation. But, mapping terms is a complex, labor-intensive process. The goal of this work is describe and understand the challenges and develop tools to overcome them.