The purpose of the Planned Development - Mixed Use District is to promote areas appropriate for office, retail, and residential uses, designed in a unified and cohesive manner in order to create an attractive environment in which to live, work, and recreate. Two or more uses shall be integrated into a mixed use project. The district is intended to be established in areas suitable for redevelopment and identified within the Comprehensive Plan as opportunity areas numbered 3 and 5, along East Nelson Street and South Main Street, respectively, and to provide a process and design criteria that can be used to transition from established uses while accommodating new growth and evolving market trends. Development proposals should incorporate high-quality architectural design and provide gradual transitions to surrounding land uses. The opportunity areas designated along East Nelson and South Main Streets are also designated as entrance corridors, and development rezoned to PD-MU should protect and enhance the City's attractiveness in compliance with Article VI of this chapter. Vertical combination of uses is encouraged where appropriate, and a PD-MU is expected to produce a better design than can be produced through traditional zoning districts.