In Ethiopia, a 20-day house-to-house GIS mapping exercise conducted in Jigjiga town (Somali region) between August and September 2024 revealed major discrepancies between projected and actual target populations: official estimates placed the HPV-eligible girl population at 6,770, while the headcount identified 11,300 — a 67% undercount — and 14,935 girls were ultimately vaccinated, representing 132% of the original projection. Zero-dose child counts were similarly underestimated, with 16,777 identified against a projection of 11,778, of whom 86.6% were vaccinated following the exercise. GPS-linked data collected via SurveyCTO enabled spatial visualisation of target population clusters and informed the establishment of seven new urban health posts to address physical inaccessibility of existing facilities. The findings demonstrate that house-to-house GIS mapping is a high-yield microplanning tool for closing equity gaps in HPV vaccination, particularly for out-of-school girls and zero-dose children in rapidly urbanising settings.