Unity Navigation (NavMesh, Pathfinding, AI)

Overview

Unity's AI Navigation package (com.unity.ai.navigation) bakes a NavMesh -- a simplified walkable surface -- and provides NavMeshAgent to move characters along it. This is the standard solution for AI NPCs in the generated project.

Baking a NavMesh

Mark static colliders as Navigation Static (Window > AI > Navigation > Object).
Bake the NavMesh (Window > AI > Navigation > Bake).
At runtime, every NavMeshAgent on the scene automatically walks on the baked NavMesh.

For a procedurally generated city, baking at design time is impossible. Either:

Bake at runtime via NavMeshSurface.BuildNavMesh() (AI Navigation package), or

Use the simpler approach in NPCController.cs: pick random points via NavMesh.SamplePosition so the agent always lands on a valid walkable spot.

NavMeshAgent

[RequireComponent(typeof(NavMeshAgent))]
public class NPCController : MonoBehaviour
{
    private NavMeshAgent _agent;

    private void Awake() => _agent = GetComponent<NavMeshAgent>();

    private void Start()
    {
        PickNewDestination();
    }

    private void PickNewDestination()
    {
        Vector3 random = transform.position + Random.insideUnitSphere * 20f;
        if (NavMesh.SamplePosition(random, out NavMeshHit hit, 20f, NavMesh.AllAreas))
            _agent.SetDestination(hit.position);
    }
}

Key properties:

Property	Meaning
`speed`	Max movement speed (m/s)
`angularSpeed`	Max turning speed (deg/s)
`acceleration`	How quickly the agent reaches `speed`
`stoppingDistance`	Distance at which the agent considers the destination reached
`autoBraking`	Whether to slow down near the destination
`isStopped`	Pause the agent without clearing the path
`remainingDistance`	Distance to the end of the current path
`pathPending`	True while a new path is still being computed

State machines for AI

A common pattern is a small finite state machine:

Idle  --(timer)-->  Wander  --(player in range)-->  Chase
  ^                    |                                 |
  |     (lost sight)   +---------------------------------+
  +--------------------+

The generated NPCController.cs implements exactly this pattern with three states (Idle, Wander, Chase) and switch-based dispatch in Update().

Pathfinding details

NavMeshAgent.SetDestination(target) is async -- the path may not be ready on the same frame. Check !agent.pathPending before reading remainingDistance.
agent.pathStatus tells you whether a path is PathComplete, PathPartial or PathInvalid.
NavMesh.CalculatePath(source, target, mask, out path) lets you compute a path without an agent (useful for "can the NPC reach this point?" checks).

NavMeshObstacle

For dynamic obstacles (a car parked across a road, a door that closes), add a NavMeshObstacle component. Set carve = true to actually cut a hole in the NavMesh; otherwise the obstacle only pushes agents around.

Off-mesh links

When the walkable surface is disconnected (e.g. a gap between rooftops), drop an OffMeshLink to let agents jump or teleport across. You can also use them for ladders, climbing walls, and jumping down from ledges.

Performance

Keep the agent count under ~100 simultaneous active agents on desktop.
For larger crowds use the ECS/DOTS navigation solutions or batch pathfinding across frames.
Set agent.autoRepath = false if you do not need the agent to follow moving targets, and call SetDestination less often (e.g. every 0.5 s).