Offline maps for phone and smart watch: Topographic maps, satellite images, GRIB weather forecast maps and road maps with cycle and hiking trails.
Nautical charts are currently only for USA and Canada available.

Please watch the video and read the FAQ:
http://www.MapChartMosaic.com/

Switch seamlessly between maps from different sources to get detailed information about a location.

Map views are automatically stored in an offline cache on your phone, so that you can view them later without an internet connection.

Download offline maps to your smart watch and view them without connection to your phone.

Add map markers and notes to the offline maps (e.g. your current car parking location).
Create travel routes. Record your GPS Track.
Share map marker, route and track data as GPX files.
Get GPS travel info: speed, course, odometer, route ETA (estimated time of arrival)...

Get GRIB weather forecast maps via Internet download, Email or Iridium Go satellite connection.

You can display the maps also on your Wear OS smartwatch.
The smartwatch app Map Chart Mosaic can be used without a connection to your phone.
But you need the phone app Map Chart Mosaic to download new map charts, map marker and map routes to your smartwatch.

DISCLAIMER
Do NOT use the app for navigation or any other purpose that may result in personal injury or property damage. Use it at your own risk.