Map download

GMAD Files:
To get the workshop id, you need to go to the addon page and copy the page url. At the end you will find a string of numbers. That is the workshop id. Example: https://steamcommunity.com/sharedfiles/filedetails/?id=152413570
steamcmd +force_install_dir <gmod_server_location> +login anonymous +workshop_download_item 4000 <workshop_id> +quit
This will download it to your server location, printed by the command. You will either get a gma or bin file.
If you get a gma file, then you can use gmad. Like so:
gmad extract -file file.gma -out .
But if it's a bin file, then you need to do it like so:
7za x file.bin
mv file file.gma
gmad extract -file file.gma -out .
7zip will give you an error, but still a extentionless file. You just rename it to have a gma ending and then like normal with gmad.
Software/Sites:
https://github.com/Facepunch/gmad
https://www.ezyzip.com/open-extract-gma-file.html
https://steamworkshopdownloader.io/