Final answer:
The Battle of Mactan was greatly influenced by geographical features such as rocky outcroppings, corals, and shallow waters, which hampered the Spanish forces' ability to land and ultimately contributed to their defeat.
Step-by-step explanation:
The major geographical causes that had the biggest impact on the Battle of Mactan were primarily the rocky outcroppings, corals, and shallow waters which impeded the Spanish forces from landing near the beaches. In April 1521, when Ferdinand Magellan, supported by Spain, reached Mactan Island, his ships could not approach close to the shore due to these natural barriers. The inability to land troops directly and efficiently on the beaches was a key factor that led to the defeat of Magellan and his forces at the hands of Lapulapu's warriors.