The indirect method of contouring is a surveying technique used to represent the topography of an area by drawing contour lines, which connect points of equal elevation. Unlike the direct method, where surveyors physically locate points of specific elevations on the ground, the indirect method relies on establishing a framework of surveyed points whose elevations are known.
Based on the provided reference, the indirect method involves the following steps:
- Selection of Guide Points: A series of guide points are chosen across the area to be contoured.
- Elevation Determination: The elevation of each selected guide point is accurately determined. This is often done along a system of straight lines or a grid.
- Plotting Points: These guide points are then plotted on a map or plan according to their surveyed positions and determined elevations.
- Contour Drawing by Interpolation: Contour lines are drawn between the plotted points by interpolating between the known elevations. This means estimating where a specific contour elevation would lie between two points of known, different elevations.
Key Aspects of the Indirect Method
The reference highlights several advantages of using the indirect method:
- Quicker: The field work of establishing and surveying guide points is generally faster than tracing specific contour lines on the ground.
- Cheaper: It tends to be more cost-effective due to reduced time and labor requirements in the field.
- Less Laborious: The overall effort involved, especially in the field, is less compared to the direct method.
This method is particularly useful for large areas or rough terrain where the direct tracing of contour lines would be impractical or very time-consuming. The accuracy of the final contour map depends heavily on the density and accuracy of the initial guide points and the precision of the interpolation process.
