Section 8. When a town has been divided into voting precincts or the voting precincts thereof have been changed, the selectmen shall post in the office of the town clerk and in at least three public places in each new precinct a map or description in which the new precincts shall be designated by numbers or letters, and defined clearly and, so far as possible, by known boundaries. They shall furnish copies thereof to the registrars of voters and the assessors of such town, and to the election officers of each precinct so established.