(a) The planning commission shall have the duty of preparing a zoning plan, including both the written provisions of the ordinance and a map or maps showing the district boundaries. The commission may hold such public hearings as it deems necessary concerning the zoning ordinance. It shall certify the zoning ordinance and map to the county commission. On receipt of a zoning ordinance and map from the county planning commission, the county commission shall hold a public hearing thereon, after which it may adopt the zoning ordinance and map as recommended, adopt it with modifications, or reject it.