Showing the alignment grid
The alignment grid helps you align items on a diagram. You can snap items to the grid.
To show the alignment grid
1. On the Model tab, click Options.
2. On the Tools Options dialog, click the Diagrams entry.
3. Select the Show Alignment Grid check box.
* 
When working on a diagram, you can show or hide the alignment grid by selecting or clearing the Show Grid check box in the Format menu.