Final answer:
A solid blue line on a VFR sectional chart represents the boundaries of controlled airspace, where pilots may need to comply with specific flight rules and communicate with air traffic control.
Step-by-step explanation:
On a VFR sectional chart, a solid blue line indicates the boundaries of controlled airspace. Controlled airspace is an area where air traffic control (ATC) services are provided. These areas are designed to facilitate a safe and efficient flow of air traffic, and pilots flying in these areas may be subject to certain flight rules and may need to communicate with ATC.