2. How Do We Construct Maps Using Isolines What are Isolines?

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

4. Examples of isolines: Isotherms: points of equal temperature Isobar: points of equal barometric (air) pressure Contour: points of equal altitude Anything else you can get a value for. (The weather channel loves isolines!)

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

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

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

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

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

10. 6. On a field map, isolines that cross a stream make a V-shape. The Vs always point upstream. In the diagram below, the Vs point toward the northeast. This means the stream is flowing to the southwest. N

11. Visualizations of contour lines http://geology.asu.edu/~sreynolds/topo_gallery/t opo_gallery.htm

13. Gradient Gradient shows how quickly the value changes from one point to another.

14. 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. Making Contours worksheets Worksheets can be printed from: http://www.rcmurphy.net/Medina%202005/docu ments/Contours123.doc

16. Find the 60 data points; Connect all 60 value data points.

17. Highlight data points.

18. Fill in gaps in data.

19. Connect the dots.

20. Go on to the next value.

21. Making a Contour Map II

23. Drawing Contour Maps III