Hi user_5359,

These mass imports are coming in the following of the Zanzibar Mapping Initiative (https://opendri.org/project/zanzibar/)
A drone acquisition campaign was used to build up a database of buildings.
The license is OdBL.

One of objectives is to help the Commision for lands in land registry using OSM.

BRN is a reference ID for each building and zone is a grid number used for acquisition.

Contact me with in private if you want a contact with the project leader.

Hope that this answer is ok,
Pierre-André Le Ny