Final answer:
Alvarez de Pineda's voyage in 1519 was significant for mapping the Texas Gulf Coast, which provided Spain with important geographical knowledge of the region, distinct from the explorations conducted by others in areas like Florida or the southeastern United States.
Step-by-step explanation:
The voyage of Alvarez de Pineda most helped the Spanish learn about the Texas Gulf Coast. While other explorers such as Hernando de Soto and Juan Ponce de León explored other areas like Florida and what is today the southeastern United States, Alvarez de Pineda's exploration was significant for mapping the coastline of the Gulf of Mexico, including the Texas coast, in 1519. His expedition filled in vital geographical information that was previously unknown to the Spanish, marking a pivotal moment in the efforts of Spain to understand and claim the lands that lay to the north of their Caribbean colonies.