The contour interval depends upon the nature of the terrain (Table 17.1). For flat ground, a small contour interval is chosen whereas for undulating and broken ground, greater contour interval is adopted.

Table 17.1 Contour Interval ( CI) for different types of Survey

Sl. No	Purpose of survey	Scale	CI (m)
1	Building site	1/1000 or less	0.2 to 0.5
2	Town planning, reservoir etc.	1/5,000 to 1/10,000	0.5 to 2
3	Location Survey, earthwork, etc.	1/10,000 to 1/20,000	1 to 3