When you create a tilemapA GameObject that allows you to quickly create 2D levels using tiles and a grid overlay. More info
See in Glossary in an existing Grid GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary, it is possible to try to create a tilemap that uses a different Cell Layout to the Grid. If this happens, Unity detects the mismatch in the Cell Layouts and a dialog appears. The dialog prompts you to decide if you want to continue creating the child tilemap or stop the action.
Select Continue to continue creating the child tilemap, and Unity changes the parent Grid’s Cell Layout to match the child’s. Alternately you can select Cancel to stop creating the new child tilemap.
Note: If you are running the Unity Editor in headless mode, this dialog won’t appear and the Editor creates the tilemaps automatically as if you have selected Continue.