Radiation Method

The radiation method of the Plane table offers a straightforward approach to surveying. Unlike its more complex counterparts, the radiation survey method doesn’t require intricate calculations or a plethora of sophisticated equipment. Instead, it relies on a well-established principle – measuring distances and directions – to build a map one feature at a time.

radiation method of plane table survey


  1. Set up the Plane Table:
    • Choose a central location (P) with a clear view of the features you want to map.
    • Set up the plane table on a tripod and level it using the levelling head and plumb bob. Ensure the board is horizontal.
  2. Orient the Plane Table (Optional):
    • If you want to show a north arrow on your map, use the drawing compass to orient the long edge of the drawing board in a north-south direction. This step is optional but helpful for overall map clarity.
  3. Set Up the Alidade:
    • Attach the alidade to the plane table, ensuring it moves smoothly along the straightedge.
  4. Mark the Station Point:
    • On the drawing sheet, make a small pinprick or mark a point to represent your current location (instrument setup). This is your station point P.
  5. Sight and Draw Rays for Features:
    • Identify a feature you want to map, a ranging rod is shown in the figure (it can also be a tree, corner of a building, etc.).
    • Sight the alidade towards the ranging rod, ensuring the object is centred in the alidade’s sight.
    • With the alidade locked in position, draw a line from the station point outwards along the straightedge of the alidade. This line represents the direction from the instrument to the feature.
  6. Measure and Plot the Distance:
    • Walk with the tape measure to the targeted feature.
    • Measure the horizontal distance between the station point and the feature.
    • Choose a map scale (e.g., 1 cm represents 10 meters).
    • Using the measured distance and chosen scale, measure the corresponding length on the alidade’s ruler.
    • From the station point on your drawing, carefully mark this scaled distance along the ray you drew earlier. This marks the position of the feature on the map.
  7. Repeat for Additional Features:
    • Repeat steps 5 and 6 for all the features you want to map from this station point.