The lesson focused on understanding lines on a map, specifically lines of latitude and longitude, and their significance in finding locations on the globe. Key concepts covered include the Equator at 0° latitude, the Tropic of Cancer (23.5°N), the Tropic of Capricorn (23.5°S), the Arctic Circle, and Antarctic Circle at 66.5° both north and south. Additionally, the Greenwich Meridian, also called the Prime Meridian at 0° longitude, and the International Date Line were discussed.