Urban drainage infrastructure such as culverted waterways, minor canals, and stagnant water catchments is among the hardest features to map in OpenStreetMap, yet its absence quietly undermines spatial analyses across multiple risk domains. This lightning talk documents a YouthMappers-led effort to systematically improve drainage network completeness in OSM, motivated by two converging applications: flood exposure modeling and dengue risk analysis.
We present practical methods for identifying, validating, and mapping physically hidden or under-represented drainage features using open geospatial workflows, and show how improved coverage meaningfully changes analytical outputs for both hydrological and public health applications. The talk closes with transferable lessons for community mapping programs targeting infrastructure that is present on the ground but invisible in open data.