Overview

Layers are what make most image editors so powerful. Images are stacked on top of each other in the layers list. You see a flattened version of the layers in the canvas. If you take the text tool and write something on your image, you will notice that a new layer called a shape layer has been created. By using the move tool, you can move around this layer without affecting the layer underneath. Similarly, if you apply a filter it will only apply to the layer you currently have selected in the layers list. Using this properly will give you the best possible results, and will also allow you to be more flexible if you want to change something later. When in doubt, make a new layer.

Hiding and Renaming Layers

Layers can be hidden and renamed in the layers list. From left to right you can see a visibility mark (the eye), picture of the layer, and the title of the layer. Toggling the little eye next to the thumbnail layer will hide and display the layer, leaving all the other layers visible. Layer names can be changed at any time by selecting the layer then clicking on the existing text. 

Pro Tip: To hide all other layers, select the layer you want to remain visible then hold down the option key while clicking the eye. To return all the layers to visibility hold down the option key while clicking the eye again.

Adding, Deleting, Selecting, and Duplicating Layers

Adding & Deleting: Navigate to the Layer... menu item and you will find options to create a new layer (⇧⌘N), a new shape layer , and to delete the currently selected layer (^⌘-). An additional keyboard shortcut to delete the currently selected layer is ⌘⌫.

You can also right click (or control click) on your layers list to bring up a contextual menu with the options to create and delete layers. Below the layers list, there is a plus button. The plus button will create a new bitmap layer. On the bottom righthand corner there is a garbage can. Clicking this will delete the currently selected layer.

Selecting: To select a single layer in the layers list, just click on it. To select multiple layers you can hold down the command key while clicking on each layer you want selected. To select a range of layers, click on the first layer you want selected then hold down the shift key while clicking on the last layer you want selected.

Duplicating: To duplicate a layer, select that layer in the layers list. You can then right click on the layers list to bring up the contextual menu, or you can choose Layer ▸ Duplicate Layer from the menu. An additional method is to hold down the option key while clicking the '+' button in the inspector palette.

Grouping Layers

You can group layers together by creating a group layer in your layer list. A group layer works just like a folder. You can create a group by right-clicking inside your layers list to bring up the contextual menu, or you can choose the Layer ▸ New Group Layer menu item. An additional method is to hold down the command key while pressing the '+' button in the inspector palette. 

If you have multiple layers selected and want to put them in a group, you can use keyboard shortcut command-g. If you have a group layer selected and would like to ungroup it, then use keyboard shortcut command-shift-g.

A folder icon will appear in your layers list. You can now drag your layers into this group layer. Notice there is an disclosure triangle next to the visibility icon. Clicking on this triangle will show or hide all the layers within this group.

You can rename the group folder by double-clicking the name and entering your own. Grouping layers is also a good way to move multiple layers at once.

Pro tip: If you have a group layer selected and you use the Edit ▸ Copy menu item, you will get a composite of the entire group layer on the clipboard.

Locking Layers

Locking layers is useful if you have an object on a layer that you do not wish to move. Locking the layer it rests upon will prevent you from making unwanted changes. 

To lock a layer, right click on the layer you wish to lock. Then select "Lock Layer" from the menu. This is also available under Layer ▸ Lock Layer.

You will notice that a small lock icon appears in the right side of the layer.

Use the same process to unlock the layer.