The City Council shall divide the city into six wards in all, and may change the boundaries of such wards, but no changes will be made within three months prior to an election: Provided, that no change in the boundaries of the wards shall affect the term of office of any Councilman, but he shall serve out his term in the ward in which his residence may be at the time of his election. The representation of each ward in the City Council shall be as near as may be in proportion to population. No person shall be eligible to the office of Councilman unless he shall reside at the time of his election in the ward for which he was elected, and the removal of a Councilman during his term of office from the ward for which he was elected to another ward in the city, or outside the city, shall render his office vacant.