on this page: moving vs. extruding | how to
When you move, or translate a selected polygon, the polygon moves to the position specified by dragging. When you extrude a selected polygon you are not moving it, but duplicating it so that when it is moved, new sides form connecting the polygons. So when you extrude a polygon and then move it, the surrounding polygons stay the same shape; compare this to how the surrounding polygons change shape if you do not extrude the polygon first. For example, if you create a house with a chimney and move the selected polygon before extruding it, here's what will happen:
Not quite the right thing.
But when you move the polygon after extruding it, a nice rectangle shape is formed:
Just right for a chimney.
Note that this example uses Extrude Polygons .
If you had used Extrude Edges
instead, the chimney would have no top:
Trick: If you accidently use Extrude Edges, you can close the top:
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