topomap wallpaper decorative image(Link to original image found here) (Links to

topomap wallpaper decorative image(Link to original image found here) (Links to an external site.)
This week we are going to cover topographic maps. This lab is going to be different in that the material on this lab will not be covered in any of the normal lectures. It is important that you not only finish this lab, but that you try to understand the materials because there will be questions about topography on the test. If there is anything you do not understand, don’t hesitate to ask. You may work in groups, but everybody will need to turn in their own assignment. If you work in groups, please list everybody’s name at the top of the lab report.
Watch the Video linked here (Links to an external site.) as David Oliver, Adjunct Instructor discusses the concepts behind topographic maps, and reviews this lab.
For your reference, download a copy of the power point slides referenced in the video download.
Download the Lab Report found here downloadto record your responses. When you are finished, upload your lab report using the Canvas button. Let your instructor know if you need help uploading your assignment.
Yosemite map found in your college provided at-home lab kit. (If you have not yet obtained your lab kit, links to the digital form of the map are located at the end of this lab.)
Purpose and Goals
The purpose of this lab is to familiarize you with reading and interpreting topographic maps. Topographic maps are valuable tools in geology. They are also used by hikers, hunters, campers, and others who need to know the topography of a given area.
For example, imagine you were hiking in Arizona near Bumble Bee Creek on the the BCT Trail and all you had was similar to the map below. After this lab, you would be able to tell how many feet above sea level you would travel along this trail (which could help you infer whether or not you need to take breaks along the way to avoid altitude sickness… it’s a thing! Look it up!) and the various features of the landscape you might see along the way (hills, steep slopes, valleys, roadways, waterways, etc.). Don’t panic! We’ll walk through this together. =)
Bumble Bee Creek and BCT Trail topographic map image
(Link to original image found here) (Links to an external site.)
A topographic map is a two-dimensional representation of a three-dimensional landscape. Historically, the development of highly accurate, detailed topographic maps has largely been driven by military requirements. A unique characteristic that distinguishes topographic maps from other kinds of maps is the fact that they show the topography, or shape of the land, in addition to other features such as roads, rivers, lakes, etc. Because topographic maps show the shape of the land, they are the most suitable type of map for most outdoor activities that take place in areas that are not heavily populated. Hence, in order to study landscape features, we use a topographic map. The key to using topographic maps is understanding contour lines. Each contour line connects places that have the same elevation or height.
Another way to think about those lines is like this:
elevated topography map puzzle-like image
(Link to original image found here) (Links to an external site.)
Every contour line on a topographic map is a different elevation. We don’t necessarily know what the slope looks like (or how quickly the elevation changes) between each of those lines (unless we’re physically standing there and feel like calculating it, but that’s a lot of work!), so think of these lines like puzzle pieces that are stacked on top of eachother. If we took just one of those hills and sliced it down the middle, then connected those contour lines from the side, it might look a little like this:
countour lines and interval example
…but in reality, that’s just playing “connect-the-dots;” the slope could actually change around that hill more than what is shown in that drawing. It could be more of a jagged line rather than a smooth line or it could drop suddenly and then level out. The point here is that between the contour lines is just a guess, so if you are asked for the elevation between two contour lines, estimate a number between the two contours surrounding it. The average slope is what we assume in geology.
You might notice that on the left side of the graph, there is something called the contour interval. That is simply the difference between the two contour lines on the map. You will notice that the controur lines are always the same interval apart on each map you look at. In this one, the interval is 20 (we don’t know if that is in feet or meters, though, since we weren’t given a map key!). In other maps, it could be 100 or 200 or 500; it varies from map to map.
Most topographic maps in the United States are published by the United States Geological Survey (USGS) in the form of quadrangles. A quadrangle is a section of the Earth’s surface that is bounded by lines of latitude (north and south) and longitude (east and west). The most common sizes of quadrangles are 15-minute and 7 ½ minute quadrangle maps. These numbers refer to the amount of area covered in degrees of latitude and longitude (there are 60 minutes per degree). Therefore, a 7 ½ minute quadrangle covers an area 7 ½ minutes latitude by 7 ½ minutes longitude. One 15-minute quadrangle can be divided into four 7 ½ minute quadrangles.
All quadrangles are oriented such that geographic north is toward the top of the map when the text (title, etc.) is right side up. Note that geographic north is not the same as magnetic north, or what you would read from a compass. Geographic north is the location of the Earth’s rotational axis at the North Pole. Magnetic north refers to the magnetic polarity of the Earth’s magnetic field and wanders regularly. The angle formed between the direction of geographic north and magnetic north is referred to as the magnetic declination. It is usually included on quadrangles in the lower margin.
A topographic profile is a cross sectional view along a line drawn through a portion of a topographic map. In other words, if you could slice through a portion of the earth, pull away one half, and look at it from the side, the surface would be a topographic profile. In the rough cross section image below, we literally cut the map through points A and B, rotated it 90 degrees, then simply connect(ed)-the-dots!
Topo 01.gif
Topography – study of the shapes and features of the earth’s surface
Contour line – connects places on a map that are all at the same elevation
Contour interval – the difference in elevation between neighboring contour lines
Elevation – height above or below sea level
Bench mark – a point that has been accurately measured for its position and elevation
Magnetic declination – Since the geographic North Pole and magnetic North Pole of the earth do not coincide, the north arrow on a topographic map often shows the difference between true north (TN) and magnetic north ( Map Scale – Many people have built or seen scale model airplanes or cars that are miniature representations of the actual objects. Maps are similar in that they are “scale models” of the earth’s surface. Maps have scales that expresses the relation between distances on the map to the true distance on the earth’s surface.
Topographic Profile – A topographic profile is a cross sectional view along a line drawn through a portion of a topographic map. In other words, if you could slice through a portion of the earth, pull away one half, and look at it from the side, the surface would be a topographic profile.
Slope – The average slope of a hill can be measured by measuring change in elevation between two points and dividing that by the horizontal distance between two points.
Some Rules Regarding Contour Lines
Contour lines follow some basic rules. If you understand contour lines, you should be able to explain why each of these rules is true:
The closer spaced contour lines are, the steeper the ground surface is.
Contour lines never cross
Contour lines never branch
Contour lines never change elevation
Contour lines never skip (e.g., you can never have the sequence of lines 10, 20, 40 without having 10, 20, 30, 40)
Contour lines always have an up side and a down side (all elevations on one side of the line are higher than the line, all elevations on the other side lower). The up and down side never change along the length of the contour line.
Contour lines will always point in the upstream direction. This is sometimes called the “Rule of V’s” because the expression of a river on a contour map causes the contour lines to “V” in the upstream direction. Refer to the video for an example of this.
Answer each of the following groups of questions in your own words on your lab report. (In case you get stuck on anything below and need a little bit more assistance in learning how to read topographic maps, check out this link (Links to an external site.).)
General Topographic Questions
What is a contour line?
What is a contour interval?
How does the scale of a map differ from the values of contour lines? (i.e., what is each measuring?)
What do closely spaced contour lines indicate?
Why is it important to know the magnetic declination of a map?
Interpreting a Topographic Map (Mount Saint Helens)
Refer to the topographic map of Mount Saint Helens below to answer the following questions on your lab report.
Topographic map of Mt St Helens with legend
What is the elevation at point C?
What is the elevation at point D?
What is the elevation of the benchmark on the map?
What is the contour interval of this map?
Sketch a rough topographic profile of the transect between points A and B (the dark line on the Mount Saint Helens topographic map).
Interpreting Topographic Profiles
Match the topographic shape on the left to the profile on the right on your lab report.
Topo 4 A.gif
Applying what we have learned
Use the topographic map below to answer the following questions on your lab report.
Atwater topographic map with legend
How many benchmarks are there on the map?
What elevation values do they mark?
What is the highest elevation indicated anywhere on the map and what is the lowest elevation indicated anywhere on the map? (Review the video linked above for a hint!)
What elevation does the highest contour line represent?
What is the elevation (or approximate location) of the following points?
point A = _____ feet
point B = _____ feet
point C = _____ feet
point D = _____feet
Explain why you can determine the exact elevation for points A and B but only approximate elevations for points C and D?
What is the contour interval for this topographic map?
Which stream flows into Atwater Pond?
Which stream flows out of Atwater Pond?
How can you determine what direction the streams, from the question above, are flowing?
Calculate the slope of the hill from point G to point E. NOTE: You must show your work.
Use the contour lines to find the elevation difference between the two points.
Use the map scale to measure the horizontal distance between the two points. If you need assistance with this, check out this link. (Links to an external site.)
Calculate the slope which is the change in elevation divided by the horizontal distance between the two points.
Calculate the slope of the hill from point B to point F. NOTE: You must show your work.
Compare the slopes from the calculations you made above. Points G to E are on the north side of the hill, why are the contour lines closer together on the north side of the hill while they are further apart on the south side of the hill (Points B to F)?
Now, open your Yosemite Valley map from your college provided at-home lab kit, then answer the following questions. Please note that if you have not yet obtained your lab kit, the map is linked at the end of this lab.
What is the ratio scale for this particular map?
What is the contour interval on this map?
Locate Half Dome toward the east side of your map. Which side of Half Dome is steepest?
How long did it take you to complete this lab?
…And now you’ll never be this hiker…
McFarland flat map comic
(Link to original image found here) (Links to an external site.)
Links to maps in case you have not yet obtained your lab kit
Yosemite Valley online pdf version of map linked here (Links to an external site.).
Yosemite Valley map in pdf form to save to your computer linked here downloadPreview the document.
Don’t forget to upload your saved and completed lab report!

Laser Cutting a Topographical Map

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