topography for land and sea maps

[kdarras]

We need to be able to choose different base layers for the map.

In particular, bathymetry and elevation should be shown so that we can show a global topography map.

Some information is here: https://wiki.openstreetmap.org/wiki/Bathymetry and an example can be found here: http://www.openseamap.org/

[kdarras]

this source looks excellent but does not seem reachable with an API to extract tiles: https://www.ncei.noaa.gov/products/etopo-global-relief-model

[kdarras]

Otherwise, Mundialis? https://leafletjs.com/examples/wms/wms.html