Topographic Maps lab .docx
pdf
keyboard_arrow_up
School
University of Minnesota-Twin Cities *
*We aren’t endorsed by this school
Course
1101
Subject
Geography
Date
Jan 9, 2024
Type
Pages
8
Uploaded by BarristerElementMink31
Introduction to Online Topographic Maps
Directions:
Open this file in word, and type your answers into the spaces provided using BLUE or GREEN text
(so I can find your work easily amongst the questions). Save this completed lab and upload it to the
appropriate assignment folder on D2L
The purpose of this lab exercise is for you to become familiar with the information presented on a digital
topographic map and how to interpret that information.
Learning Objectives:
Interpret information included in a topographic map
Measure distance on a digital topographic map
Determine precise coordinates
Determine elevation and elevation changes on a topographic map
Equipment required: - Download and install these first if you don’t already have them on your
computer!!!!!!!!!
Computer with internet access
Adobe Acrobat Reader (available free at
http://get.adobe.com/reader/
) (although most computers have
a pdf reader already available/installed)
Background:
Contour maps have lines (called contour lines) that connect points of equal-ness (be that
elevation/temperature/thickness/etc.). You look at contour maps fairly often without realizing it. Below are
contour maps of daily high temperatures across the US. The one on the left is color coded with purple/blue
colors being cooler temperatures and orange/red being warmer temperatures. If you took away the
coloring and just left the outlines of colored areas you would have something that looks more like the
diagram on the right (obviously showing a different time of year…but you get the idea). On these maps,
the contour lines are connecting points of equal temperature.
Page | 1
Topographic maps are another type of contour map. Instead of connecting points of equal temperature
like in the above maps, we connect points of
equal elevation
with the
contour lines
.
Contour lines show
hills, valleys, mountains, plains, and the like. This is a way for us to take our 3 dimensional world and turn into
a flat, 2 dimensional object but still keep the 3 dimensional information.
They not only show us the
horizontal distribution of features like any street map you may be more familiar with looking at would, they
also show elevation differences across the land surface. In other words, it is a way for us to still see where all
the mountains/hills/valleys/etc. are by looking on a flat piece of paper. Typical topographic maps are not
color coded for elevation, but just use the contour lines (similar to the contour map on the right above).
Elevations on topographic maps are given in feet or meters above mean sea level. The shore of a lake is,
in effect, a contour line because every point on it is at the same level (elevation).
Here are a set of pictures showing how the
contour lines translate into shape of the
land surface. The top drawing shows a side
view of a hill with contour lines, the bottom
drawing shows the topographic map of the
same hill. Note how the two drawings
relate.
You can clearly tell the image to the left is a human
face. By contouring the points of equal elevation
across the face, we see where the highs and lows are
even though this is a two dimensional image without
any shading to aid in viewing the 3D aspects of a
face.
Page | 2
Systematic mapping of the topography of the United States did not begin until after 1884. The task was
assigned to the newly created United States Geological Survey (USGS). Mapping was originally based
almost exclusively on field surveys and hand sketching of contour lines based on surveyed control points in
the field. It wasn’t until after the world wars that the field of photogrammetry was developed. Large
swathes of territory could be quickly and more accurately mapped by use of aerial images. Pairs of images
with significant overlap taken from slightly different angles created a three-dimensional “stereoimage” from
which elevation could be determined.
Topographic maps were originally created at 1:250,000 scale and later 1:62,500 (15 minute series) scale.
With the use of photogrammetry, and the demand for more detailed maps, the USGS began creating the
much more detailed 1:24,000 (7.5 minute series) scale map series. The 1:24,000 scale is the most popular
map scale now produced by the USGS. Mapping of the contiguous 48 states at 1:24,000 scale was
completed in 1991.
In 2001, the USGS released “The National Map”, an online platform to display and distribute geographic
data to users. The National Map consists of eight data layers: transportation, hydrography, boundaries,
structures, geographic names, land cover, elevation, and orthographic images. Digital versions of
topographic maps were released via The National Map in 2009 as geoPDF files and include a variety of
layers, such as aerial imagery, that can be toggled on or off. The 7.5 minute series maps are now updated
every three years as new aerial images are collected for the National Agricultural Inventory Program. The
USGS is currently in the process of digitizing all topographic maps created prior to 2009.
Some basics on contour lines
●
They connect points of equal elevation
●
Steep slopes are shown by closed spaced contour lines
●
Gentle slopes are shown by widely spaced contour lines
●
Contour lines never intersect, branch, or cross. They may merge in a vertical or overhanging cliff
●
When contour lines cross a stream, they bend upstream; they form a “V” shape with the point of
the V pointing upstream
●
Closed contours appearing as circles or ovals represent hills or knobs
●
Closed contours with hatch marks (short lin
●
es pointing toward the center of the closure/circle) represent closed depressions. The outermost
hatched circle will have the same elevation as the adjacent regular contour line.
Contour line patterns
Scale information:
Scale is given in a number of ways on the map. Either as a visual scale bar like this -
1
½
0
1mile
Or as a fraction like this – 1:24,000
Page | 3
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
In which case, this means 1 unit of measure on the map equals 24,000 units of measure in real life.
It’s basically the number of times you have shrunk real life to make it fit on the map. In this case, that would
be 24,000 times. It is a unitless number. So 1cm on the map = 24,000cm in real life, 1” on the map = 24,000”
in real life, 1 hand width on the map = 24,000 hand widths in real life, etc. You will be playing around with
understanding map scale a bit today on the two maps on your table.
Other map information includes the contour interval – always written somewhere on the map, usually near
the scale and the name of the map.
This video is just over 11 minutes long and does an excellent job of explaining how to read and interpret a
topographic map – this was part of the pre lab work, so hopefully you have watched it already!!
https://www.youtube.com/watch?v=bENEygui4jo
Page | 4
Exercises:
Reading a geoPDF topographic map
Posted to D2l is a map file labeled “MN Bloomington map for lab activity”. Download this and open it.
Upon opening the map, you should see a topographic map with an aerial image overlay
– be patient, this
is a large file and can take a bit of time to open!
If you were wanting to find this map (or any other map) on your own for future use, here’s how: Navigate to
http://nationalmap.gov/ustopo/
and click on the green box labeled “Get maps” then the “launch” button
to download topo maps of the US. Now you can search along the top of the map that appears and use
this get current and historical topographic maps for any location within the United States. Search for
“Bloomington, MN” using the search bar. Click on “find products” in the text bubble that appears on the
map. On the left hand side you will have options for US topo and historical topo maps to download.
Maps contain a lot of information about location, scale, etc. on the bottom of the map page. Scroll down
to here (and zoom in if needed!) to answer the following questions.
1.
What is the scale of the map?
1:24 000
2.
What is the contour interval of the map?
10 feet
3.
What is the name of the quadrangle map immediately west of the Bloomington quadrangle?
saint paul south west
4.
What is the date (year) for the map?
2010
This gives you an idea of what an actual paper map would look like, if you were sitting in a lab classroom.
But it’s hard to make actual measurements on this without special toolbars (that can be downloaded and
used, but there aren’t any currently freely available that work well on both Macs and Windows
machines…)
Let’s look at the actual map now, instead of the legend information.
Choose the correct answer in the following sentences
5. Contours along steep slopes, such as edges of river valleys are
[(closer together than)
(farther apart than)
(the same distance apart as)]
contours in flatter areas such as valley floors.
Find Nine Mile Creek on your map (see the annotated map below).
Page | 5
You will find the elevation change of Nine Mile Creek between the two thin red circle locations on the map
- where Nine Mile Creek crosses Normandale Blvd (NW of campus) Ave, and north of where Nine Mile
Creek crosses Old Shakopee Blvd (SE of campus) – by answering the following questions (see the
annotated image below the questions with help on finding elevations using topographic lines). Note: these
two circled locations should show up on the pdf map you download and open from D2L as well.
6. What color are the topographic (topo) lines on this map?
brown
7. What is the approximate elevation of Nine Mile Creek where it crossed Normandale Blvd (remember,
the creek is not right on a topo line, so it can’t be the same elevation as the nearest topo line – you’ll have
to estimate!)? Make sure you include units!!
700 m
8. What is the approximate elevation of Nine Mile Creek at the location north of Old Shakopee Road
(again, it’s not right on a topo line, and include those units!)?
750m
9. What is the elevation change of the creek between the Normandale Blvd and Old Shakopee Rd circled
locations?
50m
Page | 6
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
10. Which direction is Nine Mile Creek flowing (i.e. NW, S, NE, SW, etc.)?
South east
Here is an annotated image on how to go about finding elevation using topographic lines (not the same
map you have, but the principle is the same):
Page | 7
To find the slope or gradient of the creek is the same as finding the gradient or slope of a hill – which you
had to practice last week. So the formula is still the elevation changed divided by the distance over which
we see that elevation change. In the case of a creek, that distance is not a straight line because the
creek winds across the landscape. If we had a paper map, we would take out a piece of string and lay it
along this path matching all those curves in the creek’s path and then straighten out the string to get that
full distance. If we had capable drawing tools (also part of what is hard to find in software that works on all
possible computer types students might be using!), we could draw a path and then measure the length of
that path. We don’t have that option here, so I will just tell you that the length of Nine Mile Creek between
the two points (Normandale Blvd and Old Shakopee) is about 4 miles long.
Using the length of the creek (given above) and the elevation change you calculated (question 9), you
can calculate the gradient, or slope, of Nine Mile Creek along this segment of its path, from Normandale
Blvd to Old Shakopee Road.
𝑆𝑙??? =
?𝑙?𝑣𝑎?𝑖?? ?ℎ𝑎?𝑔?
?𝑖??𝑎??? ??𝑎𝑣?𝑙𝑙??
11. What is the slope of this segment of Nine Mile Creek? This will be in units of feet per mile – make sure you
include the units in your answer!
50 m / 9mi = 5.5 m/mi
12. Look around now at where the Minnesota River runs through the Bloomington area. What is the
approximate elevation of the Minnesota River Valley (not the river itself, but the valley floor)? You can use
the predominant labeled topographic contour line. Make sure you include units!!!
200m
13.
How high above
the Minnesota River Valley are the Pleasant View Memorial Gardens (located south of
the river and east of 35W) as measured from the “G” in the word “Gardens”(there is a contour line that runs
right under the “G”)?
70m
Page | 8