“…Designs with many levels are desirable, but it is not essential to keep the number of runs equal to the number of levels. These designs are quite suitable for practical use, and in addition, they can be viewed as stepping stones to space-filling design as a good space-filling design must be column-orthogonal or nearly so (Bingham, Sitter, and Tang (2009) ;Sun, Pang, and Liu (2011);Georgiou, Koukouvinos, and Liu (2014); Yuan, Lin, and Liu (2017)). …”