The predesigned containers in Visio 2013 expand automatically when you add shapes near the edge of the container. You can change this default behavior by using the Format tool tab of the Container Tools tool tab set: in the Size group, click the Automatic Resize button to reveal three mutually exclusive options.
No Automatic Resize The container will not expand when you drop shapes near the edge.
Expand as Needed The container will expand when you drop shapes near the edge. The opposite is not true: however, the container will not shrink when you remove shapes.
Always Fit to Contents The container will expand and contract automatically when you add or remove shapes.
You can also affect container size with the two buttons located above and to the left of the Automatic Resize button shown in the preceding graphic: