The NavMeshes in different ScenesA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary are not connect by default. When you load another level using Application.LoadLevelAdditive() you will need to connect the NavMeshes in different Scenes using an Off-Mesh link.
In this example we have Scene 1 and Scene 2. The Scene 1 has an Off-Mesh Link starting over a walkable area and landing over a walkable area in Scene 2. There can be as many Off-Mesh Links connecting the Scenes as necessary.
When authored the other end point of the scene connecting Off-Mesh links are not connected. After a new Scene is loaded, the Off-Mesh Links will be reconnected.
If the multiple scenes have NavMeshA mesh that Unity generates to approximate the walkable areas and obstacles in your environment for path finding and AI-controlled navigation. More info
See in Glossary overlapping at the same area, the position picking may be arbitrary NavMesh at that location. This applies to agents, Off-Mesh Links and position picking using the NavMesh API. You should create the scene crossing Off-Mesh links so that they start and end clearly on over one NavMesh only. Overlapping NavMesh areas are not automatically connected.