here is the links
https://support.modeltrainstuff.com/entries/22809918-What-are-the-different-Gauges-and-Scales-What-do-they-mean- (https://support.modeltrainstuff.com/entries/22809918-What-are-the-different-Gauges-and-Scales-What-do-they-mean-)
http://www.railserve.com/Models/Layouts/HO_Scale/ (http://www.railserve.com/Models/Layouts/HO_Scale/)
http://rrmodelcraftsman.com/extraboard/cm_extra_scenerytipsandtechniques.php (http://rrmodelcraftsman.com/extraboard/cm_extra_scenerytipsandtechniques.php)