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Topographic Maps Notes
 

Topographic Maps Notes

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    Topographic Maps Notes Topographic Maps Notes Presentation Transcript

    • Earth ScienceEarth Science Reading TopographicReading Topographic MapsMaps
    • Definition of Topographic Maps 1. A graphical representation of the three dimensional shape of the earth’s surface that shows: a) elevation b) shape
    • Features of Topographic Maps (not on notes page…) TOPOGRAPHY (RELIEF): - printed in brown - contour lines shows hills, mountains, plains, etc. WATER FEATURES: - printed in blue - includes oceans, lakes, ponds, rivers, canals, etc. CULTURE: - printed in black - human-make works such as roads, railroads, buildings, land boundaries, etc.
    • Features of Topographic Maps Relationship between 3D and 2D representation 3D view 2D view
    • Key Terms: Topography: general shape of the Earth. Elevation: distance above sea level. Contours: lines of equal value. Contour line: is an imaginary line on the surface of the earth connecting points of equal elevation.
    • Contour lines Relationship between topographic features and contour lines
    • Contour interval (C.I.) is the difference in elevation between any two adjacent contour lines. x Relief: the difference between the highest and lowest elevation in a particular area.
    • ADD to your notes page: Contour index- extra dark line with numbers.
    • If we put contour lines on the island every 10 meters, it would look like this…
    • Now, let’s determine the elevation at several points of the island… 0 – sea level 10 meters ~15 meters +20 meters, but < 30 ~8 meters
    • General Features of Contour Lines Topographic Maps can show: ELEVATION: 1.Contour lines connect points of equal elevation.
    • Topographic Maps can: Show if the land is STEEP or GENTLE: 2. Steep slopes are shown by closely spaced contour lines. 3. Gentle slopes are shown by widely spaced contour lines. Contour lines do not intersect, branch or cross.
    • Topographic maps can: Identifying RIVERS and STREAMS and their FLOW: 4. When contour lines cross streams they bend upstream; that is, the contour line forms a 'V' with the apex at the intersection with the stream, and pointing in an upstream direction.
    • Topographic maps show: If there is a HILL or DEPRESSION: 5. Closed contours appearing on the map as ellipses or circles represent hills. 6. Closed contours with hatchures, short lines pointing toward the center of the closure represent closed depressions.
    • TOPOGRAPHIC MAPS: DEFINITIONS Freebies: #3 – gradient #4D – profile Bottom of page #7 – solid, intermitted For numbers 1 – 4 (a – d) Choose from these words: Contour line Depressions Elevation Index Interval Topographic map For numbers 1 - 8 at the bottom, choose from these words: Gentle hill hill lowest never sea level Steep hill upstream
    • Answers: 1. Topographic map 2. elevation 3. Gradient 4. Contour line a) Interval b) Index c) Depression d) profile 1. Never 2. Hill 3. Steep 4. Gentle 5. Upstream 6. Sea level 7. Solid, intermitted 8. lowest
    • Write down: Rules to determine the contour interval (with multiple lines):  Find the difference between the two INDEX contours (a).  Count contour lines between the contour indexes, then add one (b).  NOW DIVIDE (a/b)
    • A. Contour Interval? B. C. D. E. The difference in elevation between the two index contours (800 - 700) is 100. We cross five lines as we go from the 700 line to the 800 line (NOTE: We count the lines between the index contours, then ADD one. In this case, we have 4 lines + 1 = 5). Therefore is we divide the elevation difference (100) by the number of lines (5) we will get the contour interval. In this case it is 20. 720 m 740 m 760 m 780 m
    • 2. Determining a value of a depression…  Determine the outer ring’s value.  Outer ring is = to the lowest valued contour line.  In a depression – elevation DECREASES as you go towards the center. 1. Determining a value of a hill…  Determine the outer ring’s value.  Outer ring is = nearest lowest valued contour line PLUS contour interval.  In a hill– elevation increases as you go towards the center.
    • p Row 1 10 30 10 30 20 0
    • Row 2 20 180 200 1400 5 +25
    • Row 3 100 1400 5 35 200 4400
    • Row 4 1 7 200 2400 100 400
    • Topographic Profiles DEFINITIONS - A topographic profile is a diagram that shows the change in elevation of the land surface along any given line (an area “looked from the side”). - Gradient - The steepness of a slope as measured in degrees, percentage, or as a distance ratio (rise/run). - Change in elevation between 2 points/length of measured 2 points. When dividing, make sure the units are the SAME!!!
    • Vertical exaggeration (VE) Topographic profiles are usually constructed with some amount of vertical exaggeration (VE) to emphasize the details of topography. The VE is determined by the following steps: 1 . Determine the number of feet represented by one inch on the vertical axis of the topographic profile. In Figure 7-7C one inch represents 100 ft or 1:1200. 2. The horizontal scale of the profile is the same as the map, 1:24,000. 3. The VE is calculated by dividing the horizontal scale by the vertical scale. VE = horizontal (map) scale/vertical scale VE = 24,000/1200 VE = 20x The VE of 20 indicates that the topography illustrated in Figure 7-7C is exaggerated by 20 times that of the original map.
    • How to Make a Topographic Profile This represents a very simple topographic map of a hill. The hill is steep on the left side (the contour lines are very close together) and has a gentle slope on the right side. The numbers represent the elevation of the contour lines. (*) 100 200 300 400 What would the hill look like if you were to slice it from left to right? (*)
    • 100 200 300 400 500 feet 400 feet 300 feet 200 feet 100 feet Normally, the Earth’s surface is not this blocky. In a topographic profile a line is drawn from these points (red dots) producing a smooth transition. (*) Thus you have a topographic profile. This is what the hill would look like if you were to cut it along the profile line and look at it from the side. (*)
    • Topographic Profile
    • Topographic Profile Constructing a Topographic Profile
    • A B 6400 The contour interval of this map is 40 feet. Every index contour would then be 200 feet. 8000 7000 7600 7400 7200 7800 6800 6600
    • A B 6400 The contour interval of this map is 40 feet. Every index contour would then be 200 feet. 8000 7000 7600 7400 7200 7800 6800 6600 In this region the profile line cut across the 7800 foot line 4 times. (*) The last step is to simply connect the “dots”. (*) The profile is finished. (*)
    • A B 6400 The contour interval of this map is 40 feet. Every index contour would then be 200 feet. 8000 7000 7600 7400 7200 7800 6800 6600 This is a very classic example of a butte with steep sides and a very flat top. The profile that you see here is an exaggerated scale – the vertical scale is greater than the horizontal scale. The next example is where the vertical scale is closer to the horizontal scale. (*)
    • THE GRAND CANYON, ARIZONA This view of the Grand Canyon is from the South Rim looking north into Bright Angel Canyon. This is what it looks like on a topographic map. (*)
    • THE GRAND CANYON, ARIZONA This view of the Grand Canyon is from the South Rim looking north into Bright Angel Canyon. This is what it looks like on a topographic map. (*) It may not be as majestic but it is full of information. (*)
    • Let’s take a look at this area from a topographic point of view. (*)
    • Cumberland, Pennsylvania/Maryland This area is in the deeply eroded folds of the Appalachian Mtns. What type of drainage pattern is shown in this area? (*)This a very good example of a TRELLIS PATTERN. The tributaries come in from the hills and meet the main channel at almost 90o . (*) The tributaries are shown in blue and the main channel is shown in violet. What stage in the cycle of stream erosion do these streams display? (*)
    • Cumberland, Pennsylvania/Maryland Just for fun, let’s construct a topographic profile across the main stream from point A to point B. (*) AA BB Try to visualize what this profile would look like before you move on. (*)
    • Cumberland, Pennsylvania/Maryland AA BB Using every INDEX CONTOUR – 100 foot interval … (*) 1100 1000 900 800 700 600 Stream Now just connect the dots and draw a smooth profile. The stream occupies the lowest point of the valley. (*)