Each block should have a base point that is logically positioned for inserting the block in relation to other geometry in a drawing; that is, the base point location should allow the user to insert the block using an object snap on some other piece of geometry as an insertion point. If possible, the base point location should also facilitate repeated placement of the item. For example, a block representing a paver should not have the base point in the middle of the block, because you would not likely want the middle of the block inserted at any object snap on existing geometry. Likewise, a base point in the upper-left corner only makes sense if the item is to be placed under some other geometry. However, if the base point is at the lower-left corner, the user can snap to the ground plane, and repeated insertions are easy.