Placement

Placed items are those that have become fixed parts of the world, requiring a Tool in order to free and pick up. This is in contrast to inventory items or dropped items. Items can be "naturally placed" by the game, which most commonly occurs when a world is first generated. Items can also be placed by the player: When a player builds structures, they are placing items such as Blocks and Furniture.

Placement layers
As far as the player experience goes, placed items fall into several "layers" laid over the map, with a little overlap; the most obvious distinction is that the first layer represents "foreground" objects that can block the player's movement, while the others represent various "background" layers, with little or no effect on the player's passage.


 * Foreground: A foreground object is something that collides with the character and inhibits movement. The vast majority of these are blocks, and in turn nearly all blocks are placed in the foreground layer. There are a few non-blocks in the foreground layer, such as Boulders and Teleporters, and a few objects (e.g. Doors, Platforms) that can interact with both this and the next layer. Thorny bushes and their variants are among the few plants in the foreground, but Living Trees are also made of foreground blocks.
 * Actuators can turn most foreground objects into background ones (and back again) but actuators cannot force a "native" background object into the foreground. The Active/Inactive Stone Block has the ability to shift between foreground and background state when prompted by wire signals.


 * Background: A background object is something that does not collide with characters, but cannot share a tile with a foreground block. (This is sometimes called the "furniture layer".) Characters can move through them freely. These include the majority of plants (trees, vines, tall grass, etc), and almost all furniture. Many background objects are for visual appeal only, though several, such as crafting stations and storage items, have functions for the player.
 * Some objects possess qualities of both the foreground and furniture. Doors are foreground objects when closed and background ones when open. Some furniture (especially Platforms) are mainly background objects, but a character can stand on top of them (Pressing the key causes the character to fall through them). Aside from platforms, many of the "flat surface" furniture items act like this: Work Benches, Tables, and the like.  Bubble blocks act like solid blocks with respect to liquids, but otherwise as furniture items.
 * Liquids: Liquids occupy their own layer: While they normally flow around blocks and can not be placed in them, blocks can be placed in liquids (except lava) and the liquid is then trapped but not destroyed. A few furniture objects can similarly trap liquids (chests), but normally liquids can flow through background objects, perhaps breaking them in passage. Liquids will slow the passage of characters and most projectiles. With appropriate accessories or buffs, players can walk on the surface of a liquid as if it were a platform. Liquids can partly or completely hide furniture-layer items they cover, as well as characters or enemies within them.


 * Wiring: The "wiring layer" contains Wire and Actuators; these can overlap and interact with foreground or background objects, and never collide with the character or other entities. They are not visible unless the player is either wielding a mechanism-related object, or else using a Mechanical Lens or The Grand Design. When such wiring objects are visible, they are not concealed by objects on any other layer. Note that most other mechanisms are either foreground objects or background furniture.


 * Walls: Walls do not impede objects on any other layer, but they can provide "support" for placing foreground or background objects. Otherwise they do not interact with other layers, and are depicted behind every other layers and before biome backgrounds. Natural walls can affect biome determination and enemy spawning. Some walls can spread their respective biomes to adjacent walls, but never to blocks.


 * Biome background: The biome background is the "bottom" placement layer of a Terraria world; every other layer exists on top of this. It can only be interacted with using a World Globe or Monoliths, both of which changes it. Some settings also affect it.

How to place
There are two ways to place items:


 * If Autopause is off and the Inventory is open, the player can pick an item from the inventory and press the button at any point where the item can be placed.
 * Regardless of autopause, if an item is in the player's Hotbar, a player can select it as one would a Weapon or Tool, and press the button at any point where the item can be placed.

In either case, this must be done while the mouse cursor is in an appropriate spot for placement of the particular item, and while the player is within a few tiles of the placement location.

For example, most Furniture items, like the Work Bench, must be placed on a flat surface of at least several blocks in length. With the Work Bench item selected in the Hotbar, move the mouse cursor to just above a relatively long, flat surface, clear of any other items (grass included), and press the button.

In most cases, a Pickaxe is used to free a placed item so it can be picked up again. As a special case, natural trees (including Cactus and giant mushrooms) require the use of an axe to harvest them. Note that anything requiring an axe to harvest cannot be directly placed by the player.

For items with left/right orientation such as beds and chairs, the direction the character is facing at the time of placement determines which way the item is placed.

Requirements for placement

 * An item must be "placeable". Most, but not all items are placeable. Whether or not an item is placeable is indicated within the game via its tooltip; items that say 'Can be placed' when the player hovers their mouse cursor over them are placeable.


 * The placement area must fit the particular item. While Blocks can be placed in any empty space adjacent to any other Blocks, Furniture items generally have more stringent placement requirements. Most require a solid, flat surface, while some are more versatile (like Torches), or more demanding (like Doors or Candles). After 1.3.0.1 Update, it's easier to find appropriate placement area, using Placement Preview option found in Interface Options.

Function of placed furniture items

 * Placed crafting stations, like the Work Bench and Anvil, expand the player's crafting menu when the character stands near them. The current crafting options can bee seen by opening the inventory and looking at the bottom-left corner of the screen. Scroll through the craftable items with the mouse wheel. Different crafting options will appear depending on which crafting station the character is near at the time.


 * Placed storage items allow the player to store and retrieve items by using them with the key. Any Dresser will also give access to a menu affecting player appearance.
 * Placed background walls will allow NPCs to move into the player's structure, and in many cases, will prevent Enemies from spawning in a structure. See NPC and House for more details on this.
 * Placed background walls will also allow some furniture to be placed on, like Switches, Levers and Torches.
 * A placed Bed allows a player to set their own spawn point.