This ongoing empirical study suggests a model for evaluating a combination of environmental risk factors to explain neighborhood differences in adult use of Harlem Hospital's Asthma Emergency Department services. A multilevel or "nested" model incorporates methods for hypothesis testing using geographic information systems (GIS) and existing data from Harlem Hospital Center, city agencies, and other sources to measure variables on both building and street segment levels. Selection of the best geographic scale by which to measure housing conditions, neighborhood physical quality, income indicators, and access to healthcare is an important strategy toward identifying neighborhood socioenvironmental patterns contributing to geographic clustering of asthma emergencies. Specific community interventions may then be defined to improve the health outcomes of residents with asthma.