TerraFirma is a map viewer often used for compiling images of large worlds and structures. It also displays extensive block and world information as you pan around the map. Due to this, another common use is to scour the world for naturally occurring Ores, Statues, Chests, and other world features.
Terrafirma - Terraria Map Viewer01:04

Terrafirma - Terraria Map Viewer