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## Topographic Maps

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**Topographic Maps**• Maps of an elevation field • Show elevation by contour lines • Also show other natural and man-made features by using symbols**1. Contour lines – lines the connect points of**equalelevation**Steep slope**Gentle slope • Contour Lines close together – • Contour Lines far apart –**2. Contour Interval** The contour interval on this map is 20? What do you think is a contour interval?**Contour Interval**Change in elevation in between two consecutive contour lines Usually listed in key or legend**If you are at sea level, your elevation is 0.**The contour line for the coastline is 0.**3. Index Contour Line**• The Index Contour lines on the map below are the 700 and 800 lines Why do you think they are darker?**Index Contour Lines**• Every 4th or 5th line that is thicker or bolder • Line is labeled with the elevation • Helps to read the map** What is the spacing of Index Contours on this map?** What is the contour interval?**4. Hills**• How is a hill depicted on a topographic map?**Hills**• Closed contours in a circle or elliptical (oval) shape • “Bulls eye”**5. Depressions**• The opposite of a hill is a depression which is a low point in the ground. They are represented by hachure lines. Describe what a hachure line looks like. Feathered line or a line with hash marks**5. Hachured Lines**• Does the elevation go up or down when you see the hachured lines? • The first depression line is going to the ________ elevation as the closest contour line down same**6. Benchmark - EXACT Elevation**Indicated by a BM or X on a topographic map**What is the exact elevation of the benchmark on this map?**2919 feet**7. Streams always flow Downhill – from higher elevation**to lower elevation Can a stream flow northward? Yes**N**What direction is this stream flowing? South**N**Describe what the contour lines look like when they are crossing a stream? Contour lines point in the opposite direction the stream is flowing!**Streams always flow in the opposite direction the V or U is**pointing.**8. Maximum Elevation of a Hill**Steps to follow: 1. Count up the contour lines using the contour interval. 2. Pretend that there is one more contour line at the top of the hill (imaginary line). 3. Subtract 1**How is the highest possible elevation?**Highest contour line = 40 Pretend one more so that would be 50 Subtract 1 50 – 1 = Maximum elevation of hill is 49**9. Minimum Elevation of a Depression**Steps to follow: 1. Count down the contour lines using the contour interval. 2. Pretend that there is one more contour line at the bottom of the depression (imaginary line). 3. add 1**Map Scales**• The relationship between distance as measured on a map and the actual distance on Earth’s surface**Types of Map Scales**• Verbal Scale – 1 inch = 20 miles • Bar Scale One Mile**Types of Map Scales**c. Ratio Scale - One of any unit on this map represents 24,000 of the same unit on Earth’ s surface.Ex, one inch would equal 24,000 inches on the Earth**Maps often give you more than one way to measure distance**Represents one mile on the map Represents parts of one mile, ex: one tenth of a mile One kilometer