【Unity】Mastering Layers and Tags: Smart Object Classification and Management in Unity

Overview

As you progress in Unity game development, the number of GameObjects in your scene quickly grows. Players, enemies, items, terrain, UI elements—when hundreds or thousands of objects coexist, you often face problems like:

1. Performance degradation: Unnecessary physics calculations (collision detection) occur between all objects, slowing down processing.
2. Inefficient searching: Finding specific types of objects (e.g., all enemies) from scripts takes time.
3. Rendering complexity: Cameras attempt to render objects they shouldn't.

To solve these problems and improve both development efficiency and game performance, Unity provides powerful object classification and management features called Tags and Layers.

This article explains how professional Unity developers differentiate between Tags and Layers, from basic concepts to practical techniques like collision detection control and efficient object searching, with concrete code examples.

Tags: Use as Object "Identifiers"

Tags are identification labels that can be attached to GameObjects. They are most commonly used to easily find specific types of objects from scripts.

Basic Tag Usage

To set a tag, select an existing tag from the dropdown at the top of the Inspector, or create a new tag from "Add Tag...".

The biggest advantage of tags is the ability to search for objects very intuitively from scripts.

using UnityEngine;

public class TagSearchExample : MonoBehaviour
{
    void Start()
    {
        // Search for one object with "Player" tag in the scene
        GameObject player = GameObject.FindWithTag("Player");
        if (player != null)
        {
            Debug.Log("Found player object: " + player.name);
        }

        // Search for all objects with "Enemy" tag in the scene
        GameObject[] enemies = GameObject.FindGameObjectsWithTag("Enemy");
        Debug.Log("Total enemies: " + enemies.Length);
    }

    // Example of identifying the other object using tag during collision
    private void OnTriggerEnter(Collider other)
    {
        // If the collided object's tag is "DamageZone"
        if (other.gameObject.CompareTag("DamageZone"))
        {
            Debug.Log("Entered a damage zone!");
            // Reduce player HP here, etc.
        }
    }
}

GameObject.FindWithTag() searches the entire scene, so calling it frequently can impact performance. Search once in Start() or Awake() and cache (store in a variable) the result; avoid using it in every frame's Update().

Layers: Use for Functional "Grouping"

Layers, unlike tags, are primarily used for functional control. The two most important uses are:

1. Physics calculation (collision detection) control: You can set specific layers to ignore collisions with each other.
2. Camera rendering control: You can set cameras to render only specific layer objects, or conversely, not render them.

Optimizing Collision Detection with Layers

The most powerful use of layers is collision detection control. For example, if collisions between "background objects" and "background objects" are unnecessary, you can significantly reduce physics calculation load by setting them to the same layer and disabling collision.

1. Create Layer: Create a new layer (e.g., Background) in Edit -> Project Settings -> Tags and Layers.
2. Apply to Objects: Apply the Background layer to background objects.
3. Disable Collision: Open Edit -> Project Settings -> Physics (or Physics 2D), and uncheck the checkbox where Background and Background intersect in the Layer Collision Matrix.

Layer	Default	Player	Enemy	Background
Default	✔	✔	✔	✔
Player	✔	✔	✔	✔
Enemy	✔	✔	✔	✔
Background	✔	✔	✔	(Uncheck)

With this setting, objects belonging to the Background layer will not perform physical collision detection with each other even if they touch.

Optimizing Raycast with LayerMask

Layers are also very important when performing Raycast (detecting collisions by casting rays). Using LayerMask allows you to execute Raycast targeting only objects belonging to specific layers, skipping unnecessary checks and speeding up processing.

using UnityEngine;

public class RaycastExample : MonoBehaviour
{
    // Declare as public variable so it can be set from Inspector
    public LayerMask targetLayer;

    void Update()
    {
        // Cast ray forward
        Ray ray = new Ray(transform.position, transform.forward);
        RaycastHit hit;

        // Execute Raycast. Specify LayerMask as third argument
        // Here, only objects on layers set in targetLayer will be detected
        if (Physics.Raycast(ray, out hit, 10f, targetLayer))
        {
            Debug.Log("Hit object in LayerMask: " + hit.collider.name);
        }
    }
}

LayerMask type variables appear as dropdown menus in the Inspector, allowing you to easily select which layers to target with checkboxes. This method is easier to manage and less error-prone than using magic numbers (values) in code.

Common Pitfalls for Beginners

Confusing Tags and Layers

The most common mistake is confusing the purposes of tags and layers.

• Tags: Used for identification like "this is an enemy" or "this is an item."
• Layers: Used for functional control like "this object doesn't perform collision detection" or "this object isn't rendered."

By clearly differentiating—use layers when functional control (especially physics) is needed, use tags when simple identification or searching is needed—your code and settings become organized.

Bit Operations for LayerMask

When working with LayerMask in scripts, you need to use bit operations (1 << layerNumber) instead of layer numbers (0-31) directly.

For example, to target only layer number 10, write as follows:

// Create LayerMask for layer number 10
int layerNumber = 10;
int layerMask = 1 << layerNumber;

// Execute Raycast
Physics.Raycast(ray, out hit, 10f, layerMask);

This is because Unity's LayerMask is managed as a 32-bit integer, where each bit represents the enabled/disabled state of the corresponding layer. Understanding this bit operation mechanism enables advanced applications like combining multiple layers (e.g., layerMask = (1 << 8) | (1 << 9);).

Summary

By effectively utilizing Unity's Tags and Layers, object management in your scenes dramatically improves. Here are the key points covered in this article:

• Tags specialize in object identification, used for searches via GameObject.FindWithTag() and determining collision partner types.
• Layers specialize in functional control of objects, essential for optimizing physics calculations (collision detection) and camera rendering.
• Collision detection control using layers is done in the Layer Collision Matrix in Project Settings -> Physics, omitting unnecessary calculations to improve performance.
• For processes like Raycast, using LayerMask to target only specific layer objects optimizes processing.
• When working with layer numbers in scripts, the basic approach is creating LayerMask using bit operations (1 << layerNumber).

Master these fundamentals to make your Unity projects more organized and high-performing.