To support Head Start and other child health, early education, and social service providers to better understand the climate and environmental exposures children face, Urban collaborated with staff from Head Start and the US Department of Health and Human Services Office of the Assistant Secretary for Planning and Evaluation, as well as experts in child health, child well-being, and environmental and climate risks to create the Head Start Environmental Exposure Mapping Tool that models the relative exposure of Head Start children to environmental and climate hazards. This technical appendix describes the data sources and specifications, methodology, and related limitations for the feature. (author abstract)