The idea of extruding is to allow you to generate an object from a reference point, line, polygon, or surface. This is best understood if thinking about the situation where you are reading an ordinary paper map. On the map, you see one line which represents, for instance, a road. By taking extrude upon the road with a certain width and shape, and telling the extrude tool to follow the surface, the user gets a triangulated surface which gives a more visual representation of this road.

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The orientation of the extrude is done with up at screen is equal to the north at the map, while the z-axis is the zoom in the screen.

The use of the ribbon elements is further described in these links:

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