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
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!
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