Survival maps are usually about managing to survive with limited resources. They are essentially a custom experience of the survival mode in vanilla Minecraft. They often have certain objectives to complete as well.
You are living in your awesome Space House, when suddenly, alien spawners come raining down from the sky! Explore vast caves, visit 2 planets with the spaceship, watch zombies kill villagers, and more! It's all in the ultimate survival map!
Castaway is a hardcore survival map, with elements of survival island, in a different way. You find yourself stranded, on your crashed ship, in the middle of the ocean, with very few resources to start off with. Underground, are dungeons and hidden treasure with stuff you need to survive.