Surveying Methods: Simultaneous Field Observation and Plotting

Surveying is a fundamental process in civil engineering and geography, involving the measurement and mapping of land features. A key aspect of surveying is the creation of a plan or map, which is a scaled representation of the surveyed area. The timing of this plotting process relative to the field observations can vary depending on the method used.

The question asks to identify the surveying method where both the field observation (collecting data in the field) and the plotting (drawing the map) occur at the same time. This means the map is being drawn progressively as the measurements are being taken on site.

Analyzing Surveying Methods

Let's examine the options provided:

• Compass Surveying: In this method, directions of lines (bearings) and lengths are measured using a compass and chain/tape, respectively. The plotting is typically done later in the office based on the recorded field measurements. Therefore, field observation and plotting are sequential, not simultaneous.
• Plane Table Surveying: This is a graphical method of surveying. The plane table consists of a drawing board mounted on a tripod, allowing it to be leveled and oriented. Accessories like an alidade (sighting ruler with a telescope) and compass are used. In plane table surveying, the field observations (sighting points with the alidade) and the plotting of these points onto the drawing sheet are done simultaneously. As the surveyor sights a point and takes a reading (e.g., a bearing or distance), they immediately draw the corresponding line or point on the map sheet using the alidade and scale. This direct graphical representation in the field is the defining characteristic.
• Tacheometric Surveying: This method uses instruments like theodolites or total stations fitted with stadia hairs or electronic distance measurement (EDM) devices to quickly measure distances and elevations. While modern total stations allow for data logging and potential real-time mapping with connected devices, the fundamental principle of tacheometry involves taking specific readings (vertical angles, horizontal angles, stadia distances). The plotting is often done later, either manually or digitally, based on these recorded data points. It doesn't inherently involve the direct, graphical plotting *during* the observation in the same way as plane tabling.
• Chain Surveying: This is the simplest method, primarily used for small areas with simple features. It involves measuring distances using a chain or tape. All measurements are taken in the field first, and the plan is plotted later in the office using these distances and measurements. Field observation and plotting are strictly sequential.

Plane Table Surveying: The Simultaneous Method

Plane table surveying is uniquely suited for simultaneous field observation and plotting. The process works as follows:

• The plane table is set up over a station point.
• The drawing sheet is attached to the board.
• Using the alidade, the surveyor sights the next point (e.g., a station or a detail point).
• A ray representing the line of sight is drawn on the sheet.
• The distance to the point is measured (e.g., using EDM, tacheometry, or optical clinometer methods) and plotted to scale along the ray.
• This process repeats, building the map incrementally in the field.

This method is particularly advantageous for preparing small-scale maps and topographic surveys where details need to be quickly represented graphically.

Therefore, the method where both field observation and plotting proceed simultaneously is Plane table surveying.