Surveying
The difference between a level line and a horizontal line is that

level line is normal to plumb line while horizontal line may not be normal to plumb line at the tangent point to level line
horizontal line is normal to plumb line while level line may not be normal to the plumb line
both are same
level line is a curved line while hori-zontal line is a straight line

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Surveying
In triangulation surveys

Sides are not measured excepting the base line
The area is divided into triangular figures
All listed here
Control stations are located from which detailed surveys are carried out

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