Help:Surveyor Topology Radius
From TrainzOnline
Click LMB on the Radius Tool and move to either side to change the circle of influence. Move the dial right to enlarge the circle (HOTKEY “+”), left to minimize (HOTKEY “-”).
The size of the circle determines the outer limit of influence of the tool.
Whichever tool you have selected (highlighted) will be applied within the area defined by the circle.
