Depends on what you mean by communities? To HRMs government, there are communities like Bedford, Sackville, Ecum Secum, and Halifax, inside the old city of Halifax border. That is the biggest community, but I think that is garbage, as there are dozens of neighbourhoods and even old towns/villages inside of the old City of Halifax.
I think the peninsula is clearly the highest density, between 65-70 people, so most of the neighbourhoods, depending on how you define them, are as big as most towns/villages in the rest of HRM.
I did this project trying to identify old Halifax and Dartmouth neighbourhoods years ago, it just covers place names, not populations, obviously.
http://halifaxpolitics.ca/hrm-map-project/