The Mapzen elevation tilesets are on S3:

https://www.mapzen.com/blog/terrain-tile-service/

https://registry.opendata.aws/terrain-tiles/

This is the best option for free terrain tiles. There are four formats, though "Terrarium" is the most used. It maps RGB pixels in a PNG to raw elevation values using this formula [0]. If you're using Mapbox GL, you can just point your map to [1] to fetch the tiles, and then use it as a hillshade. I do that in my topographic map style [2].

[0]: https://github.com/tilezen/joerd/blob/master/docs/formats.md...

[1]: https://s3.amazonaws.com/elevation-tiles-prod/terrarium/{z}/...

[2]: https://nst-guide.github.io/osm-liberty-topo/

Additionally, the `elevatr` package (https://github.com/jhollist/elevatr) serves tiles directly from AWS Open Data Terrain Tiles. I don't believe it requires a key.

Here are a couple more ways to get SRTM tiles:

- OpenTopography (also has 3DEP/LIDAR data): https://portal.opentopography.org/datasetMetadata?otCollecti...

- SRTM 30M tile tool: https://dwtkns.com/srtm30m/

Related: in my masterclass (free and open source, materials here: https://github.com/tylermorganwall/MusaMasterclass) I also walk through how you can convert LIDAR data into hi-res DEMs to generate 2D and 3D maps

Unfortunately, SRTM 30M tile tool is asking for credentials for me.

You can also query elevation tiles using the `elevatr` package and use them in a similar way.

Mapbox has an API you can query from--I believe they have a free tier. The `ceramic` package makes this easy to pull from, but you need to get a Mapbox key first:

https://github.com/hypertidy/ceramic