Snapping helps you align layers to each other and to the center / edges of your canvas. To see a layer’s pixel distance from other layers and canvas edges, you can also enable Display Distances.
When moving multiple layers around your design canvas, you may want to have a layer equal distance to another. Now when you’re moving a layer in between others, a purple 'snap gap' will appear to show you when you’ve achieved equal distance.
Precise Pixel Measurements:
When the blue and purple snap lines appear, it means your layers have been aligned in some way. This could mean the edges line up between layers, or on the design canvas itself. You’ll notice numbers now appear along the snap lines to show the pixel distance between all of the coordinates.
Move your layers around to see them align with each other. The snap gap shows that the layers are aligned equidistant, and the blue lines show layers aligned on a vertical or horizontal axis in relation to each other.
Turn Snap Lines On And Off:
If you'd rather not use Snapping, click on the 'Alignment' menu on the Bottom Bar of your workspace. Here you can choose 'Disabled' under the 'Snapping' menu to turn it off. This will also turn off 'Display Distances' (aka gridlines).
Display Distances can only be enabled when Snapping is also enabled.
When snapping and display distances are enabled, you can use shortcuts on your keyboard to view them. Press Option on your keyboard to display distances around your current layer.