Hillier is an Associate Professor in the Department of City and Regional Planning in the School of Design at the University of Pennsylvania, and the project director for Mapping the Du Bois Philadelphia Negro. She holds a secondary appointment in the School of Social Policy and Practice, and she is a Senior Fellow at the Leonard Davis Institute of Health Economics and Center for Public Health Initiatives.
Her research focuses on issues of geographic disparities and access to services and resources in disadvantaged communities. She applies geographic information systems (GIS) and spatial analysis methods to housing and health topics. Specifically, she has studied historical mortgage redlining, affordable housing, housing abandonment, and childhood obesity. She is also interested in using modern mapping technologies to trace how birthplace and child rearing influence the opportunities available to us as adults. She has worked with Mixplace Studio, presented for TEDxPhilly (2011), and partnered with the Philadelphia Historical Society on PhilaPlace, a neighborhood and cultural history project.