So we need:
- A set of seed points, with coordinates in plan and height, in a specified datum, accurate to about 10 m in plan and 10 m in height (but this accuracy is not critical if you don’t yet have precise coordinates for the route).
- A chosen name for the grid, up to 16 characters, no spaces.
- Where separate branches are to be used, details of where the join is to be effected. This could be a coordinate, or it could be a description (e.g. “junction 1 km west of Reading station”).