In the field of surveying, different methods are employed to measure and map the features of the Earth's surface. Each method has specific characteristics and applications. The question asks for the method where field work and plotting work are done simultaneously.

Plane Tabling: Simultaneous Field Work and Plotting

Plane tabling is a graphical method of surveying in which the field work and plotting work are carried out concurrently. This means that the surveyor observes the details in the field and immediately draws them on the drawing sheet mounted on the plane table. This unique characteristic makes it distinct from other surveying methods where field observations are first recorded in a field book and then plotted in the office.

• Direct Plotting: Observations taken using an alidade are directly plotted on the drawing sheet. This eliminates the need for detailed note-taking and subsequent office plotting.
• Spotting Errors: Any mistakes in observations or plotting can be immediately detected and corrected in the field, leading to more accurate maps.
• Ideal Conditions: It is particularly effective for small-scale mapping, reconnaissance surveys, and filling in details in areas that are relatively open and free from obstructions.

Understanding Other Surveying Methods

To better understand why plane tabling is the answer, let's briefly look at the other surveying methods mentioned in the options:

Compass Surveying Methods

Compass surveying involves determining the direction of survey lines using a magnetic compass and measuring distances using a chain or tape.

• Separate Processes: In compass surveying, the angles and bearings of lines are measured in the field and recorded in a field book. The plotting work is then performed later in the office using a protractor and scale. This method does not involve simultaneous field work and plotting.

Chain Surveying Operations

Chain surveying is the simplest method of surveying, where only linear measurements are taken in the field. It is suitable for small areas with simple details and flat terrain.

• Linear Measurements First: All distances are measured with a chain or tape in the field and recorded. The entire plotting work, including drawing the survey lines and offsets, is done in the office after the field measurements are completed. Thus, it does not involve simultaneous plotting.

Levelling Techniques

Levelling is a surveying technique used to determine the relative heights or elevations of different points on or below the surface of the Earth.

• Elevation Focus: The primary goal of levelling is to establish vertical control. Readings are taken from a level instrument and staff, and these readings are recorded in a field book. Calculations and drawing of profiles or contour lines are typically done in the office. It is not a method that involves simultaneous plotting of horizontal features.

Comparison of Surveying Methods

Conclusion on Surveying Methods

Based on the analysis, plane tabling is the only surveying method among the given options where the field work and plotting work are carried out simultaneously. This efficiency and the ability to detect errors on site are its key advantages.