What is a contour map and how do I read it??

What is elevation? Elevation is the height of a geographic location above sea level. Political maps, climate maps, and road maps do not give a clear picture of the elevation of an area of land. A contour map uses CONTOUR LINES to indicate areas of steep terrain and areas of flat terrain.

What is a contour line? Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you neither gain or lose elevation.   Picture walking along a beach exactly where the water meets the land. The water surface marks an elevation we call sea level, or zero.

The contour line represented by the shoreline separates areas that have elevations above sea level from those that have elevations below sea level. We refer to contour lines in terms of their elevation above or below sea level. In this example the shoreline would be the zero contour line. It could be 0 ft., 0 m, or something else depending on the units we were using for elevation.  

How are contour lines drawn? Contour lines are useful because they allow us to show the shape of the land surface on a map.  The two diagrams below illustrate the same island. The diagram on the left is a view from the side.  The diagram at  right is a view from above (map view) such as you would see from an airplane flying over the island. The shape of the island is shown by location shoreline on the map.  Remember this shore line is a contour line.  It separates areas that are above sea level from those that are below sea level. 

How do we read the contour lines? The shoreline will always be at sea level, or 0. The lines are drawn on the map at set intervals, or spaces. These are imaginary lines! The only REAL line is the shore line. What is the interval on this map? 10!

Point A = 0 ft Point A sits right on the 0 ft contour line.  Since all points on this line have an elevation of 0 ft, the elevation of point A is zero. Point B = 10 ft Point B sits right on the 10 ft contour line.  Since all points on this line have an elevation of 10 ft, the elevation of point B is 10 ft.

Point C ~ 15 ft. Point C does not sit directly on a contour line so we can not determine the elevation precisely.  We do know that point C is between the 10ft and 20 ft contour lines so its elevation must be greater than 10 ft and less than 20 ft.  Because point C is midway between these contour lines we can estimate the elevation is about 15 feet.

Find the elevations of points D and E ~ 25 ft.We are even less sure of the elevation of point D than point C.  Point D is inside the 20 ft. contour line indicating its elevation is above 20 ft.  Its elevation has to be less than 30 ft. because there is no 30 ft. contour line shown.  But how much less?  There is no way to tell.  The elevation could be 21 ft, or it could be 29 ft.  There is now way to tell from the map.  (An eight foot difference in elevation doesn't seem like much, but remember these numbers are just an example.  If the contour lines were spaced at 100 ft intervals instead of 10 ft., the difference would be a more significant 80 ft.) ~ 8 ft.Just as with point C above, we need to estimate the elevation of point E somewhere between the 0 ft and 10 ft contour lines it lies in between.  Because this point is closer to the 10 ft line than the 0 ft. line we estimate an elevation closer to 10.  In this case 8 ft. seems reasonable.  Again this estimation makes the assumption of a constant slope between these two contour lines. Point D: Point E:

How can we use a contour map to help plan a hike? The map shows us the elevation of specific points on the map. Beginner hikers might want to take the route that is the least steep. More adventurous hikers might want to take a steeper route! You can tell how steep a hill or mountain is by how close together the lines are on the map. The closer the lines, the faster the elevation increases!