You want to minimize the transportation cost of your road, so you want the road: the smaller the distance, the better. Try to keep the level. Reduce the cost as much as possible.
This means that you need a straight road, a horizontal road, and a road that crosses several rivers and streams.
With this in mind, you actually walked (or rode)100th mile first, and recorded the compulsory points, or the points you had to use, because they had no choice.
This means that you should use your reason to find major ferries, mountain passes, and even major streams and swamps.
Therefore, you divide the road into smaller parts, for example, to reach the next stream, river or hotel.
When you can't observe rivers or streams, you need to build a tower, or choose a mountain peak or a tree in the general direction and mark a constant slope line.
The modern measuring tower in real life was built in 1902 to measure the line across Lake Superior. They are detachable and can be transported along the lake to form a survey line spanning dozens of miles. Romans could use similar towers in very flat places, such as Belgium.
Note that the former tower is a combination of two towers, one inner tower is used to support the instrument and the other outer tower is used by the surveyor, so that your movement will not affect the instrument.
Taking a tall tower or a distant mountain peak as a reference, you can mark the center line of a road or ditch by nailing piles in the soil, so as to find a long straight line.
In order to aim at the stake, you used Groma, the originator of the theodolite and total station we use today. No binoculars, just plumb lines to mark straight lines, like this one.
Roman Groma
You look at these strings as if you were aiming a gun at them.
At least two or three people are helping you.
One of the assistants holds the beginning of the chain where the metal chain groma is located (grab its copper processing image), and the other person hits the shares 10 to 50 meters away on the front and last chain according to the length of your chain.
This is an ancient measuring chain with a history of about 200 years, but in the end it uses a slightly modified Roman measuring method.
Ten ring measures one rod (about 5m) with a small bronze mark, one spike, two spikes (10m), three spikes (15m) and a full chain (about 20m).
Therefore, the measured length of 80 complete chains is slightly over 1.600 meters, which is equivalent to one mile of ancient Rome, that is, 1.000 double steps 1.6 meters each.
Mille means a thousand steps in Latin, hence the name.
The person in front stretched the chain, and then nailed the stake you told him to the ground to align him with Groma ("Right, right, right, a little to the left, there! ! "), using a rope as a visual effect.
The third assistant used a machete or similar tool to cut vegetation in front of the team to make way for the other two "chain workers", which is the name we still use to call the person who helped the surveyor.
While tracking this preliminary route, you also made a preliminary investigation and generated a map of the ground area around the route recorded in the first walk.