# Four river connections — map sources

Checked 7 September 2026. These are teaching maps of selected reaches, not complete river networks, navigation charts, legal boundary surveys or real-time flow models.

- **River linework:** [Natural Earth 1:10 million rivers and lake centerlines, version 5.0.0](https://www.naturalearthdata.com/downloads/10m-physical-vectors/10m-rivers-lake-centerlines/), public domain. The named River records were selected; manually drawn lake-centerline records are not added to conceal missing reaches. Upstream portions, reservoirs, estuaries and mouths can be omitted by this generalized dataset. A displayed endpoint is not necessarily a river's source or mouth.
- **Downstream movement:** the order of source vertices was reviewed before assigning movement. The Ohio, Delaware, Hudson, Allegheny, Tanana, Kuskokwim and short St. Lawrence reach retain source order. Three of the Yukon's five source parts (0, 1 and 3) were reversed. The Mississippi uses the previously reviewed mainstem segments; gaps remain separate. Dashes and 3D travelers indicate direction, not actual current speed or discharge.
- **Delaware selection:** the Natural Earth record includes a headwater branch. The lesson starts at source vertex 53, just downstream of Hancock's branch confluence, and retains the source endpoint upstream of the full estuary. The map does not claim to draw the entire river from its source to the Atlantic.
- **Great Lakes:** Natural Earth 5.0.0 generalized shoreline polygons retain island holes. The St. Lawrence map shows a short upper reach alongside Lake Ontario, not the entire journey to the Atlantic.
- **Surface:** [NASA Blue Marble Next Generation](https://science.nasa.gov/earth/earth-observatory/blue-marble-next-generation/base-topography/), July 2004 global topographic raster, 21,600 × 10,800 pixels. Reprojected to each regional map with a documented gamma lift of 0.70. The image is historical surface context; it does not identify current plants, snow, water levels or live habitats. A flat satellite surface tilted in 3D is not an elevation model.
- **Context:** U.S. Atlas Census-based state outlines and the previously reviewed Canadian province/territory geometry. Names and approximate location labels help orientation; they are not extra selectable river answers. These regional maps have one geographic projection each, with no Alaska-to-mainland inset travel.

The source archive, SHA-256 digest, source indices and oriented segment endpoints are retained in the project at `docs/research/boundaries/us-river-connections-ne10.geojson.gz` and `data/us-river-directions.json`. Raster digests and processing details are in `data/us-river-surface-provenance.json`.

The geography is distinct from the factual sources below each lesson: NPS for river journeys and confluences, NOAA for the Great Lakes outlet, and BLM for the Tanana's relationship to the Yukon.