Contour map – A contour line represents a single equal elevation: that is, all points on the same contour line have the same elevation.
- Where one closed contour line surrounds another, the inner contour line represents the higher elevation.
- The elevation represented by a contour line is always a simple multiple of the contour interval.
- A contour line that closes within the limits of the map indicates a hill, ridge or plateau.
- Commonly, every fifth contour line (index contour) is darker and its elevation is shown.
- On the same map, closely spaced contour lines indicate a relatively steep slope, widely spaced contour lines indicate a relatively gentle slope, and uniformly spaced contour lines indicate a uniform slope.
- Contour lines do not cross other contour lines. Exception: on a vertical cliff or a nearly vertical cliff, contour lines touch because they are on top of one another
- Every contour line eventually closes against itself. However, the map area may not be large enough to show this closure. Therefore, the contours will end at the edge of the map.
- Closed depressions are shown by hachured contour lines. The hachures point into the depression. (Hachures = short dashes)
- A hachured contour line, lying between two different contour lines, is the same elevation as the lower contour line.
- Where two adjacent contours indicate opposite slopes (hachured contour next to plain contour), both are the SAME elevation.
- Where a contour line crosses a stream or valley, the contour bends to form a “V” that points upstream or up the valley.