1. Isolines
An isoline is a line connecting points of equal value.

2. Examples of isolines: (The weather channel loves isolines!) Isotherms:
points of equal temperature
Isobar:
points of equal barometric (air) pressure
Contour:
points of equal altitude
(The weather channel loves isolines!)

5. Intervals
20 meters
10 meters

6. Rules for Drawing Isolines:
1. Isolines connect points of equal value. 5 5
10
10
10
10
15
15

7. 2. Isolines are gentle, curving lines- no sharp corners.5 5
10
10
10
10
15
15

8. 3. Isolines are always closed curves even though the map might only show part of it.

9. 4. Isolines NEVER cross- this would mean that one point has two different values. Ex: one spot has two temperatures?
60 °
50 °
40 °
30 ° X
20° Z Y

10. 5. Isolines usually are parallel. (They have a parallel trend.)

12. Rivers Rivers always flow downhill.
Isolines will show the direction the river is flowing.

13. Rivers
When a contour line crosses a river you draw a V going the opposite direction of the stream.

14. A gentle (low) gradient changes slowly and the lines are far apart.
A steep (high) gradient changes quickly and the isolines are close together.
A gentle (low) gradient changes slowly and the lines are far apart.
Steep area
Gentle area

15. Highlight data points.

16. Fill in gaps in data.

17. Connect the dots.

18. Go on to the next value.

19. Making a Contour Map II

21. Drawing Contour Maps III

23. Notice the “different” lines – Called Hachure lines
Depressions and Hills
Hills
Depressions
Notice the “different” lines – Called Hachure lines

24. Isolines that are close together show a greater gradient
Use the formula to solve for gradient
Gradient shows how quickly the value changes from one point to another.
To calculate the gradient between points Y and Z, determine their values then use a scrap piece of paper to determine the distance between the points
Isolines that are close together show a greater gradient
520 ft
490 ft
Gradient = 6 ft/mi
Distance = 5 miles