Reference

`cell.drainage`

domain: cellkind: measure

Drainage-line length + density for an H3 CELL, accumulated from OSM waterway geometry (drain / ditch / canal / nala / stream) inside the cell. This is the T2 flood-prediction sink-term input (flood-prediction.md): dense, connected drainage lowers a cell's ponding risk; undrained low-lying cells stay high. A cell measure (grain in the cell_ref) — a view of geo.hydro_feature.

Field	Type	Required	Description
`schema`	`—`	✓
`id`	`string`	✓
`cell_ref`	`object`	✓	conforms to space.cell — {h3_id, resolution, centroid?, boundary?}
`drain_length_m`	`number`	✓	total length of drainage lines whose midpoint falls in the cell
`drain_density_km_per_km2`	`number`		km of drainage per km² of cell — the sink-term signal
`segment_count`	`integer`
`primary_type`	`string`		dominant waterway type by length (drain/canal/stream/…)
`method`	`string`
`source_ref`	`string`
`layer`	`string`
`confidence`	`number`
`derived_from`	`array<string>`
`prov`	`object`	✓
`observed_at`	`string`	✓