Reference · maps
The elevation and lake-floor data behind a topographic map is free and public. Here's where to download it yourself — for the US and Canada, above the water and below it.
Land surface (the "topo" part). USGS data is the gold standard and free.
| Source | What you get | Format | Where |
|---|---|---|---|
| USGS 3DEP (via The National Map) | The standard. 1/3 arc-second (~10 m) nationwide; 1 m lidar where flown. | GeoTIFF | apps.nationalmap.gov/downloader |
| USGS EarthExplorer | DEMs including global SRTM (~30 m) and older products. | GeoTIFF | earthexplorer.usgs.gov |
| OpenTopography | Curated DEMs + raw lidar, and an on-the-fly contour-line tool. Zero install. | GeoTIFF / contours | opentopography.org |
Natural Resources Canada's CanElevation series. Search both through GEO.CA or the Open Government Portal.
| Source | What you get | Format | Where |
|---|---|---|---|
| HRDEM (CanElevation) | High-res lidar, 1–2 m, in 50 km tiles. Growing coverage. Datum CGVD2013. | GeoTIFF STAC API | open.canada.ca · HRDEM |
| CDEM (legacy) | Coarser, full-country coverage. Legacy product — what the Whistler map used. | GeoTIFF | open.canada.ca · CDEM |
| GEO.CA | The federal geospatial hub — search and map-browse all of the above. | — | geo.ca |
Canadian DEMs are usually projected (e.g. EPSG:3979 Canada Atlas Lambert) and use CGVD2013 heights — reproject to lat/lon and reconcile the datum before mixing with US data.
Lake-floor and underwater depth. No single registry exists; it comes in two tiers — surveyed (real soundings, high quality, patchy) and modeled (estimated, near-universal coverage).
| Source | What you get | Where |
|---|---|---|
| USGS ScienceBase / Open-File Reports | Per-lake survey releases (contour shapefiles, DEMs). Search by lake name. | sciencebase.gov · pubs.usgs.gov |
| USGS RESSED | Reservoir sedimentation surveys — the reservoir index (~1,800 reservoirs). | water.usgs.gov/osw/ressed |
| NOAA NCEI | Great Lakes (5 m contours) and all coastal / estuary bathymetry. | ncei.noaa.gov · Great Lakes |
| State DNRs | Often the best for ordinary inland lakes. Minnesota is the gold standard; TX, OK, WA, MA, CT, MI also strong. | MN LakeFinder + your state's portal |
| Source | What you get | Where |
|---|---|---|
| CHS NONNA | The Canadian Hydrographic Service's free non-navigational bathymetry — both marine and lake depths, 10 m / 100 m. | data.chs-shc.ca |
| Source | What you get | Where |
|---|---|---|
| GLOBathy | Modeled lake floor for ~1.4M lakes worldwide (one GeoTIFF per lake). An estimate — good for relief, not survey-grade. | figshare · GLOBathy |
| HydroLAKES | Shoreline polygons + estimated depth/volume for all lakes ≥10 ha. Pairs with GLOBathy (same lake IDs). | hydrosheds.org/products/hydrolakes |
Contour shapefiles are the easy input — each contour line is already a ready-made layer outline. With a raster DEM you generate contours yourself at your wood-sheet interval.
Two ways depth is referenced. Depth-below-surface (0, 10, 20 ft down) is tied to the water level on the survey date. Absolute elevation (NAVD88 / CGVD2013 / MSL) blends cleanly with above-water topo into one continuous surface — subtract the lake-surface elevation to get depth.
Reconcile before mixing. Reproject everything to one coordinate system, and match vertical datums (US NAVD88, Canada CGVD2013, NOAA Great Lakes MSL) or your above- and below-water layers won't line up.