Scale elements
Scale… in the context menu enlarges or shrinks the selected elements by a factor.
The Scale dialog.
The factor
You can enter it directly, or have Raily work it out: From and To take two scales, and the factor between them follows. An H0 house (1:87) headed for an N-scale (1:160) plan is shrunk to 0.544 this way, without you doing the math.
That doesn't make it an N-scale house yet
The conversion shrinks the geometry. A model built for the smaller gauge would also have fewer details and thicker walls, so it can still be printed. For the footprint on the plan the conversion is correct; for 3D printing it is a starting point.
The anchor
The anchor is the point that stays put; everything else moves toward it or away from it. The default is bottom center: whatever stands on the table stays standing on the table. If the selection has a height, the picker offers all three axes; otherwise only the area.
If you grab the wrong point, nothing is lost: move the element to its place afterwards.
What can be scaled
The entry only appears if every selected element can be scaled. If it is missing, something in the selection has fixed dimensions.
Track does not scale
A piece of track is a catalog part with the manufacturer's dimensions. A plan in a different gauge is not scaled — it is built with the track of that gauge instead, see Module selection.
Scaling a group
A group is scaled as a whole: as the parts grow, so do the distances between them. A station with its lamps keeps its proportions, instead of the lamps growing larger while staying where they were. The same applies to groups within groups.