Rules of Topographic Maps

Contour lines connect points of equal elevation; therefore, every point along a contour line is the exact same elevation.

Contour lines always separate points of higher elevation (uphill) from lower elevation (downhill).
Contour lines never cross or intersect. A point on the surface of the earth cannot be at two different elevations. An exception to this rule is, an overhanging cliff, and will be represented as dashed contour lines.
Contour lines never split or divide. An exception to this rule is, a vertical cliff where contour lines appear to merge together, but are actually stacked on top of each other.
Contour lines always close to form a shape, usually an irregular circle. Note that sometimes contour lines extend beyond the area on a map so you may not see the entire closed circle (Figure 2.16).

Closely spaced contour lines indicate a steeper slope. Contours which are further apart indicate a gentle slope (Figure 2.17).
A hill is represented by a concentric series of closed contours (Figure 2.17). The “rule of halves” can be used to interpolate the high points: add half of the contour interval to the elevation of the highest contour line.

Figure 2.17: Contour lines which illustrate steep (left) vs. gentle (right) slope (CC-BY 4.0; Chloe Branciforte, own work).

Depression contours are indicated by hachure marks on the downhill side (Figure 2.18). The “rule of halves” can be used to interpolate the low points within craters: subtract half of the contour interval from the lowest depression contour.

Contour lines “V” upstream when crossing a stream. The point of the “V” points uphill (Figure 2.19).