I came across such a witness nodes map on this tool:
https://joticajulian.github.io/steemexplorer/#/map
It looks something like this, and it seems to update in real time:
Knowing the world wide distribution of witness nodes can be a factor when deciding who to vote up, especially for big shareholders. The wider spread is the network of witness nodes, the stronger the blockchain and its resistance to attempts to coerce individual witnesses or witnesses from a certain area / country.
I understand why someone would want to keep the location of their node private, and that can also be a strength for the blockchain, as long as we have enough public knowledge of world wide coverage, like the above.
Not sure if this information helps you in any way, I found it interesting and haven't came across it in a while. So I decided to share it.
