4.1 Introduction

1. 4.1 Introduction

• The elevation of a point: vertical distance 
between point and a reference level surface 
called datum.
• Datum: If a whole series of heights is given 
relative to a plane, this plane is called a datum. In 
topographical work the used datum is the mean 
sea level (MSL)
• +ve if above MSL such as Jerusalem
• -ve if below MSL such as Jericho.
4.1 Introduction
Leveling: is the operation required in the 
comparison of heights of points on the surface of 
the earth. Its purpose to provide spot heights or 
contour lines on a map, to provide data for 
making longitudinal and cross-sections.
4.1 Introduction
Leveling can be done in several ways:
• Chain surveying
• Barometric leveling: using barometer to measure the atm. 
Pressure to determine elevation 
• Trigonometric leveling: using Theodolite
• Photogrammetric leveling: using Camera
• GPS leveling
• Differential leveling: using level and staff