The document discusses population projections created jointly by Bournemouth, Dorset and Poole to support strategic planning in the area. The three authorities purchased shared software and developed a consistent methodology to produce trend-based, policy-based, and natural change projections using national and local data. The projections are used across departments in the authorities and to inform housing and school planning. Benefits of joint work include shared resources, consistency, and cost savings, while difficulties can arise from coordinating work across different organizations.