# Coverage & datasets

> Every collection Darly serves — region, resolution, products, license — plus source ranking and vertical-datum caveats.

Browse coverage interactively in the [explorer](/explorer), or query it from
the [STAC API](/docs/stac) (`GET /collections`). Collection IDs follow
`{country}-{agency}-{program}-{resolution}`.

## Collections

| Collection ID | Region | Source | Resolution | Products | License |
|---|---|---|---|---|---|
| `usa-usgs-3dep-1m-seamless` | United States | USGS 3DEP (lidar) | 1 m | DTM | Public domain (CC0) |
| `usa-usgs-3dep-1m` | United States | USGS 3DEP per-project DEMs (lidar) | 1 m | DTM | Public domain (CC0) |
| `can-nrcan-hrdem-1m` | Canada (southern) | NRCan HRDEM (lidar) | 1 m | DTM + DSM | Open Government Licence – Canada |
| `can-nrcan-hrdem-2m` | Canada (northern) | NRCan HRDEM (ArcticDEM) | 2 m | DTM + DSM | Open Government Licence – Canada |
| `mex-inegi-lidar-1-5m` | Mexico (urban areas) | INEGI lidar | 1.5 m | DTM + DSM | INEGI Terms of Free Use |
| `mex-inegi-lidar-5m` | Mexico | INEGI lidar | 5 m | DTM + DSM | INEGI Terms of Free Use |
| `glo-esa-copdem-30m` | Global | ESA Copernicus DEM (GLO-30) | 30 m | DSM | ESA/Airbus free license |
| `glo-ogh-gedtm-30m` | Global | OpenGeoHub GEDTM | 30 m | DTM | CC-BY 4.0 |
| `sam-ufrgs-anadem-30m` | South America | UFRGS/ANA ANADEM | 30 m | DTM | CC-BY 4.0 |

Lidar collections cover their programs' published extents, not every square
meter of the country — check the [explorer](/explorer) or search the catalog
with your AOI to see what's indexed where.

## How coverage affects elevation queries

The [Elevation API](/docs/elevation) ranks candidate collections finest-first
at every location, falling through on nodata:

1. Lidar first — 1 m before 1.5 m before 2 m before 5 m.
2. The 30 m datasets last, regional before global: for `surface=dtm`,
   `sam-ufrgs-anadem-30m` answers in South America (its vegetation-bias
   correction is calibrated for the continent) and `glo-ogh-gedtm-30m`
   everywhere else; `glo-esa-copdem-30m` for `surface=dsm`.

Equal-resolution ties break to the collection with the smaller coverage
extent, so regional products are preferred over global fallbacks wherever
they apply — pass `collections` explicitly to override. The two USA 1 m
collections are the exception: the seamless mosaic always answers before the
per-project tiles it was built from, and the per-project collection fills in
where the mosaic has no coverage yet.

Queries on land within a dataset's published extent normally fall back to a
30 m global product, and queries in covered lidar areas get the good stuff
automatically. Open ocean and locations outside the selected product's extent
(including DTM queries south of GEDTM's roughly 65°S limit) return `null`. The
response's `collection` and `resolution` fields tell you which source answered.

Note the surface split: 3DEP publishes DTM only, Copernicus is DSM only. A
`surface=dsm` query in the USA falls to Copernicus 30 m; a `surface=dtm`
query almost anywhere in CONUS gets 1 m lidar.

## Vertical datums

Output datums are `egm2008` (default) and `wgs84_ellipsoid` — see the
[`vertical_datum` option](/docs/elevation#shared-options). Conversions from each
source's native datum use geoid grids with limited footprints:

- **NAVD88 grids cover CONUS only.** Sources published on NAVD88 can't be
  datum-shifted in Alaska, Hawaii, or Mexico; those pixels fall through to
  the next collection (typically the global 30 m datasets) rather than
  returning a wrong height.
- WGS84 is a datum ensemble: `wgs84_ellipsoid` heights carry roughly ±2 m of
  realization ambiguity and are not survey-grade.

## Coming next

France (IGN LiDAR HD), Germany (state programs), and New Zealand (LINZ) are
queued — the same collection contract, so `pystac-client` code and elevation
queries pick them up without changes. Want a dataset prioritized? Tell us:
[contact@darly.io](mailto:contact@darly.io).