Isolines and Topographic Maps What is an isoline? An isoline is a line connecting points of equal value.

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

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

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

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

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

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

DO NOW What is an isoline? An isoline is a line connecting points of equal value. What are isolines that connect equal points of temperature called? Isotherms What are isolines that connect points of equal pressure called? Isobars

Topographic Maps: A two dimensional map showing three dimensional land. Contour Line – - line on a map that connects points of EQUAL elevation. - show elevation and shape of the land

Topographic Maps Topographic maps are also known as contour maps. Show elevation above sea level using contour lines.

Topographic Maps Contour Interval – difference in elevation between each line. MUST be equal spacing. Contour interval = 20 feet 580 560 540 520

“Real World” Contour Map

Rules for Contours 1. Contours bend upstream (uphill) when crossing a stream.

Rules for Contours 2. The maximum possible elevation for a hill is “1” less than what the next contour “should” be. The highest possible elevation of the hill is just below the value of  the next line that is not shown 90 80 70 60 50

399 179 239

Gradient 3. Gradient shows how quickly the value changes from one point to another.

Closely Spaced Contours Steeper Slope (Gradient) – contour lines are closer together.

Wide Spaced Contours Gradual/Gentle Slope (Gradient) – contour lines are farther apart.

A B

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

Depressions 4. Contour lines which show a depression, crater, or sinkhole on a map. Shown by dashed lines on the inside of a contour line

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Rules for Contours 5. The lowest possible elevation for a depression is “1” more than what the next contour “should” be. The lowest possible elevation of a depression is just above the value of  the next line that is not shown 90 90 51 80 70 60 50

Let’s make a map!! Contour map 1

Highlight data points.

Fill in gaps in data.

Connect the dots.

Go on to the next value.

Another map!! Contour map 2

And another map!! Contour map 3