Explain methods of contouring and contour interpolation.

Contouring methods: Direct method - locate actual contour points in field by adjusting staff position until desired elevation reading obtained. Indirect method - take elevations at grid points or along features, interpolate contour positions on map. Interpolation assumes uniform slope between surveyed points. Linear interpolation: distance to contour = (contour RL - point RL) / (RL difference) x distance between points. Plot points of equal elevation and join smoothly. Use cross-sections for better contours along roads and channels. DEM software automates contouring from digital data.