Topographic maps:

Topographic maps are maps that show the configuration of the earth's surface by means of contour lines.

Contour Lines:

A contour line is an imagenery line on the earth's surface connecting points of equal elevation.

They show the shape and elevation of the land surface.

Characteristics of Contour Lines:

1. All points on a contour line have the same elevation.
2. Contour lines do not cross or divide.
3. Contour lines are always closed or endless lines. If traced troughout its entire length, a contour line ends at the exact point of beginning.
4. The inside of a closed contour line is the high side, unless dashed.
5. The ground usually rises - increases in elevation - as one away from a stream.
6. The high side of a contour line is always on the same side of the line.
7. Every fourth or fifth contour line is usually an index contour. This line is darker in color and often marked with a numerical value.
8. Land on one side of a contour line is always higher or lower than land on the opposite side, or when one crosses a contour line, he/she travels either uphill or downhill.
9. Contour lines that are closely-spaced represent steep slopes. Those that are widely-spaced represent gentle slopes.
10. The highest contour on a divide must be crossed twice without meeting any intervening higher or lower contours.
11. Maximum elevation on a map is the highest elevation.
12. Minimum elevation on a map is the lowest elevation.
13. relief on a map is the difference between Maximum elevation and Minimum elevation.  You can easily determine the local relief of an area by substracting the lowest elevation from the highest elevation.

Relief = Maximum elevation - Minimum elevation

13. Contour lines trend up valleys, cross streams, and return down the valleys on the opposite side, thus forming a V (or a U) that points upstream: A contour line bends upstream when crossing a stream and forms a V whose apex or point always points upstream.
14. In crossing a valley, the last contour met before reaching the stream is the first one encountered on the other side of the stream.
15. Gradient of a river is the elevation of point A (higher elevation) minus the elevation  of point B (lower elevation) divided by the map distance between A and B.

Gradient = { Elevation of higher point (A)  -   Elevation of lower point (B) } / Distance (AB)

16. Depression contours are used to depict creater-like closed features and bear dashes which point  toward the low side  (of the contour).
17. The numerical value of a depression contour line always indicates the same elevation of the adjacent lower regular contour line.
18. A cross section is an elevation profile of a particular part of the map.  It does not represent the whole map.