Drawing Contour Lines

One of the best ways of representing a surface on a map is by means of isolines. CONTOURS are a special kind of isoline used to represent the elevation of the surface of the earth. Contour lines join points of equal elevation on a map.

We usually start with a map of spot elevations or spot heights. The key to drawing contours is interpreting the map from the information provided. So the first thing we do is read the spot heights. Where are the high points (this would most likely be a hill), where are the low points – what pattern can we see.

There are a number of rules that must be followed when drawing contour lines.

RULES

1. Contours are drawn between two points of known value. 2. They are smooth firm lines – not angular or sketchy. 3. They never cross. 4. They never branch off. 5. They are closed continuous lines, (unless they go off the map). They never just end in the middle of the map. 6. Contour lines that form a closed circle on the map represent a HILL. 7. Contour lines that are close together indicate a STEEP slope. 8. Contour lines that are far apart indicate FLAT land. 9. Contour lines will always ‘V’ upstream. 10. The interval between isolines is called a contour interval. It is always the same on any one map. It is constant and must, by extension, include zero. 11. The value of the contour line is placed in a small break in the line, usually on the south slope.

STEP 1 1. Identify the contour interval value (10m) 2. Use pencil only! 3. Start contouring with the highest value. In this example, you will begin with 40. 4. If the exact contour interval number is on your map, draw your line through the number point. Draw your line around the numbers that have a value of 40 and above. 5. As you draw your line, look carefully when you pass between two points. Try to use your eye like a "ruler", and position the line at the proper distance between the two points. Notice the point with a footage of "38". Since 38 is very close to 40 (the contour we are drawing), you should "pull" the 40m contour over close to the 38m line. STEP 2 1. Note that you label the contour intervals for each section at the bottom (south side) of the line 2. Now that you are done the 40m line, draw the contour line for 30m 3. Leave room for your other contour lines 4. Your final contour line will have a value of zero

Finished Product! Describe in your own words what type of landform is shown