What is Rural? Examining the relationship between human populations and their inter-connectedness in the context of communicable disease transmission

Background: Rurality and urbanicity are recognized determinants of public health outcomes that influence policy and resource allocation. However, many commonly used methods to classify the rural-urban continuum, such as the Rural-Urban Commuting Area (RUCA) codes, lack applicability in low and middle-income countries (LMICs). This study introduces the Settlement Type and Road Connectivity (STARC) methodology, which offers a standardized and accessible approach to classifying regions along the rural-urban continuum. Methods: Leveraging open-source software and readily available data, STARC generates detailed maps composed of small hexagonal polygons. Each hexagon unit is assigned one of twenty-four categorical STARC codes based on its estimated population density and community-based road connectivity. Collectively, the hexagon units comprise the base layer STARC map. Additional metrics related to disease transmission can be overlayed onto each STARC hexagon unit in order to perform hotspot analysis via the local Gi* statistic and create transmission zones. All operations within the STARC process have been packaged into a publicly available tool on GitHub. Results: To demonstrate the STARC process, we executed the full STARC methology at the local, national, and regional level for study areas in Central and Western Africa. Free roaming dog densities were selected as the metric of interest in order to identify hotspots and transmission clusters for dog-mediated rabies. Conclusions: In our analysis we demonstrate that STARC codes can be used to standardize the rural-urban continuum and better understand the distribution of connectedness of populations. Hotspot analysis of free roaming dogs in several African countries shows that dog populations, a key factor in rabies transmission, are often concentrated in urban and peri-urban areas, many of which span domestic and international boundaries. By providing a dynamic and data-driven approach to understanding the rural-urban landscape, STARC offers a valuable tool for public health interventions in LMICs.