The Newburyport Redevelopment Authority has unveiled a tentative plan for improving the city’s central riverfront. Under the proposal created by Union Studio, an architectural firm based in Providence, the authority’s waterfront lots would become home to more green space and two commercial buildings, while maintaining up to 70 percent of their existing parking spaces. The 4.2-acre Redevelopment Authority property borders Market Landing Park, with about 2.1 acres on each side of the grassy park. The buildings on the site would be subject to height restrictions of about 35 feet and be placed close to the street to preserve as much open space as possible along the waterfront. Ideally, the buildings would house coffee shops, restaurants, and retail shops on the ground floors with residential units on the upper floors. To view the proposal, visit the city’s website at www.cityofnewburyport.com  and click on the link to the “presentation by Union Studio” from the home page.