From the Sky to the Garden: A Top-Down and Bottom-Up Methodology for Estimating Population Trends in Port Moresby’s Informal Settlements

Papua New Guinea’s capital, Port Moresby, is growing rapidly, and housing development has not kept pace. Thousands arrive in the city each year from rural villages, and many come to live in the city’s sprawling urban squatter settlements. The National Capital District Commission lacks reliable population data for these so-called “self-help” settlements, posing a challenge for urban planning and the allocation of scarce development resources in a fast-growing city. Utilizing publicly accessible geospatial data gathered from 18 years of aerial imagery (top-down) alongside insights from on-the-ground interviews (bottom-up), this project establishes a low-cost, mixed-methods approach for estimating population and change within a large informal settlement. The findings show how manual rooftop identification, combined with local qualitative validation, can produce robust settlement-level population estimates in data-scarce environments and illustrate context-specific limitations of automated Earth Observation-based population models in Melanesian cities. This approach is applied to 8-Mile: a well-established 2.5km2 settlement northeast of Port Moresby’s city center. Results demonstrate the practicality of this method and reveal that, despite evictions and commercial rezoning, the settlement is growing at close to double the national average and is currently home to at least 27,000 people. Overall, the study highlights the value of combining spatial analysis with community-level knowledge to support evidence-based urban governance in rapidly growing cities.