Complex sentence: The most important of these was the initiation and creation of a new and comprehensive official plan for the new city, which provided the blueprint for the future large-scale development of the City into one of the finest municipalities in Canada.
Split into simpler sentences: The most important of these was the initiation and creation of a new and comprehensive Official Plan for the new City. This Plan provided the blueprint for the future large-scale development of the City into one of the finest municipalities in Canada.