This label gives info on scale, gauge and track height. Notice that I stated the track gauge as 18" not 15". I did this to ward off any comments about no 15" rail lines in the US. The only exception being amusement park trains. I have had to explain that my 15" track represents 18" gauge. Many industries in the US used 18" gauge, such as in mining operations.
Gn15 is only 3" too narrow to represent 18" gauge. On30 is 6" too narrow to represent 3' gauge and 6" too wide to represent 2' gauge. The same goes for HOn 30.
O scale, standard gauge, trains are running on 5' gauge track, not 4' 8 & 1/2" gauge.
G scale started out, in the US, running 3' prototypes on 42" gauge track. The scale of the trans has since been enlarged to be the correct size for the track.
Many of us have to make compromises to build in a certain scale/gauge that we favor.
I've picked up a few artificial flowers from Michael's and Hobby Lobby that have the appropriate look or buds for my desert scenery. I can always spray the stuff a different color if I need to, and I hit everything with a shot of UV protection spray.
Nye, Inyo & Esmeralda Railroad