Understanding Direction Measurement in Surveying

Surveying involves determining the relative positions of points on or near the surface of the earth. A fundamental aspect of surveying is measuring the direction of lines. Directions are typically defined with respect to a reference direction, often a meridian.

What is an Azimuth Angle?

The question asks for the term that describes the direction of a line given by an angle measured clockwise from the north end of a meridian. This definition perfectly matches the definition of an azimuth.

• An azimuth is an angle measured clockwise from a reference meridian.
• The reference meridian is usually the north meridian (true north, magnetic north, or grid north).
• Azimuths range from 0° to 360°.
• Measuring clockwise from the north end means that north is 0° (or 360°), east is 90°, south is 180°, and west is 270°.

Let's look at the other options to understand why they are not the correct answer.

Analyzing Incorrect Options

Here's why the other options are not the answer:

• Parabolic curve: This term refers to a specific type of curve defined by a mathematical equation, often used in vertical alignment design for roads or railways. It describes the shape of a line, not its direction measured from a meridian.
• Contour: A contour line is a line on a map or drawing that connects points of equal elevation above a given datum. Contour lines depict topography and elevation, not the direction of a line in the sense of its bearing or azimuth from a meridian.
• Horizontal curve: A horizontal curve is used in the horizontal alignment of roads, railways, and pipelines to transition between two tangent sections. It describes the shape of a curved section in plan view, not the direction of a specific line segment measured from a meridian.

Based on the definitions, the angle measured clockwise from the north end of a meridian defining the direction of a line is indeed the azimuth.

Therefore, the correct term for the direction of a line given by an angle measured clockwise from the north end of a meridian is azimuth.

Revision Table: Surveying Direction Terms

Reviewing key terms related to direction in surveying:

• Meridian: A reference line running in a north-south direction. Examples include true meridian, magnetic meridian, and grid meridian.
• Azimuth: The direction of a line given by an angle measured clockwise from the north end of a meridian (usually 0° to 360°).
• Bearing: The direction of a line given by an acute angle (0° to 90°) measured from the north or south end of a meridian towards the east or west. Bearings are described by indicating the meridian (N or S) and the direction (E or W), e.g., N 45° E, S 30° W.

Additional Information: Types of Meridians and Directions

Understanding the different types of meridians is crucial in surveying:

• True Meridian: A line passing through the geographical North and South poles and any point on the Earth's surface. Directions relative to the true meridian are called true azimuths or true bearings.
• Magnetic Meridian: The direction taken by a freely suspended magnetic needle, influenced by the Earth's magnetic field. Directions relative to the magnetic meridian are called magnetic azimuths or magnetic bearings. The angle between the true and magnetic meridians is called magnetic declination.
• Grid Meridian: A line parallel to the central meridian of a grid system (like UTM or State Plane Coordinate Systems). Directions relative to the grid meridian are called grid azimuths or grid bearings. The angle between the true and grid meridians is called convergence.

While both azimuths and bearings represent direction, azimuths are simpler for calculations as they are single angles from 0° to 360°, measured consistently from north clockwise. Bearings require specifying the quadrant.