This document discusses population growth and characteristics in Spain. It notes that Spain's population has grown from 18 million in 1900 to 46 million currently due to natural growth and migratory balance. Some key characteristics of Spain's population include: slightly more women than men, 17% of the population under 16 years old, 66% between 16-64, 17% over 65, and around 12% of the population is immigrants. The population is unevenly distributed across Spain and is considered densely populated. The majority (80%) of Spaniards now live in urban areas compared to primarily rural in the early 20th century.