When two or more people are logged into a map at the same time, a small co-presence indicator
appears in the top right corner of the screen:
Rolling over the co-presence indicator opens a dialog box that let you learn more about, and, if you like chat with the other people listed .
(1) The Chat
link works in the same way as the Comment
button and also displays your message (temporarily) as a chat alert on the main map screen.
(2) Each person's name is displayed as a link, which, when clicked, opens the Map Community list
with their profile highlighted; from where (if they allow this) you can send them a private direct message using the Contact>>
link and/or Follow>>
their public activity stream.