This function is requested again and again (I found several inquiries on the different boards).
That would be the only plugin with this function.
A very useful feature.
For many types of websites.
The visitors would provide the information (possible directly in the frontend). This is "Web 2.0".
If only the site operator can set pins, this is "Web 1.0" ;-) .
Similar to Internet forums.
Instead of forum categories, the map is used.
You could use the existing data types.
Or (better) use an installed forum.
Each "CGM-pin" would also be a bbPress-topic (data type in a WP with installed bbPress-Forum).
So many possibilities for different types of WordPress pages.
Look at this:
("mundraub" = "theft of food")
Visitors can enter freely accessible fruit trees, berry bushes, herbs, etc..
Visitors inform if they can receive free Wi-Fi in the apartment (free WIFI hotspot in the vicinity).
Visitors inform, if in their home satellite antennas are prohibited (by the landlord).
Visitors enter their own Wi-Fi, that they want to share with others (sharing costs).
People inform about good or bad Gastronomy in the area.
And so on...