You can use the grid in Unified Modeling Language (UML) diagrams to snap diagram elements to the grid. You can also use rulers and guidelines.
With the snap-to-grid feature enabled, you can move existing diagram elements in increments based on the grid size. When you move existing diagram elements or add new ones to the diagram, the top-left corner of the shapes snap into alignment with the grid. However, enabling the snap-to-grid feature does not cause existing diagram elements to move into alignment with the grid, unless you move them after.
When you turn on the rulers, the guidelines turn on simultaneously. You can drag the vertical and horizontal guidelines, which are anchored at the upper-left corner of the diagram editor, onto diagrams and then line up diagram elements to the guidelines.