You can optionally display or hide a design grid on the diagram background and optionally have diagram elements "snap" to the nearest grid coordinate when you place or move them. Grid display and snap to grid are enabled by default.
To control grid options:
From the menubar, select Windows > Preferences.
From the options list on the left, expand the "Modeling" node, and select "Diagram."
Set the Show grid and Snap to grid options as desired.
Specify the granularity of the grid in the fields Grid width and Grid height, in pixels.
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