Question about extruding


following the “Architectural Visualization” tutorial on BlenderCookie I noticed that after extruding the vertices of the ground(which is not a quad but an ngon due to a hole that has been added for stairs) to raise the walls, the original vertices had been duplicated. Why is that? Can that lead to problems further down the road?

though i havnt seen the video, duplicating vertices can certainly cause problems. it will be best to select the whole section and select “remove doubles” from the tool bar

Duplicating the vertices in the situation you mentioned allows the ground and the walls to each have their own vertex. One reason one might wish to do this is to allow for the possibility that when the house and ground are incorporated into a larger scene, one might wish to have ability to adjust the vertices of the ground surface, without changing the wall, or vice versa.