One of the commands in the Select menu of the Picture window.
To determine where your next drawing will occur.
The "viewport" is the part of the Picture window where your next drawing will occur. You can set the colour of its margins with System Preferences → Appearance → Highlight Colour.
The inner viewport does not include the margins, the outer viewport does (see Select outer viewport...).
Normally, you select the viewport by dragging your mouse across the Picture window. However, you would use this explicit command:
© ppgb, November 8, 2004