Physical Geography Lab

LAB 2: Topographic Maps & Google Earth

Our earth is a very complex place to view as a flat map. Viewing the earth, as a globe is the best representation we can have—it is both proportionate for continental size and true in their shape. Unfortunately we cannot always keep a massive globe in our pockets, with that being said, maps must be projected. Let us first look at what the globe would look as a map if we were to lay it flat, figure 1. You can clearly identify the meridians, (lines of longitude) as well as see the fact that all meridians intersect or join at the north and south poles. If we wanted to travel through middle North America—it would be impossible to map since the globe Figure 1: Globe view with no distortion. www.ctmap.com tearing apart that location! With that being said we need to fill in the gaps using distortion. There are three dominant ways we can project the globe using distortion.

Please clearly define and match each of the following projections:

1. Cylindrical Projection:

2. Conic Projection:

3. Planar or Azimuthal Projection:

Topographic Maps

The next part of this lab will work us through some topographic maps. In modern mapping, a topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually now using contour lines, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features.

The most important pieces to a topographic map are the contour lines.

Contours

A contour line may be defined as a line on a map representing an imaginary line on the surface of the earth at a constant elevation. When following a contour line, the elevation will neither go uphill nor downhill—but remain at the same level. Contours will also never split, branch, cross over or comingle with other lines—each line has its own value and identity.

Contour interval is measured vertically, and is spaced equally in vertical measurement. The tops of hills, of course, seldom fall exactly at the contour interval—these values are often indicated by a spot elevation (see figure below).

Contour interval is the difference in elevation between two adjacent contour lines. On USGS maps, contour intervals are usually 1, 5, 10, 20, 40, and 80 feet. Occasionally you will find a map with a 25-foot contour interval or metric units, but not often. To make the contours easier to read, every fifth one is the index contour, which is printed, darker and has the elevation in feet from mean sea level marked on the line. The thinner or lighter colored contour lines are called intermediate contours.

Relief Features

Relief features are influenced by the drainage of the area. Running water works upon the surface of the ground, eroding and transporting the softer material and leaving the terrain with characteristic valley and ridge patterns. Please take note of the ‘V’ and ‘U’ shape patterns along the

contours.

4

. The ‘U’ shape pattern

suggests that the

topography is going

Downhill/Uphill

5

. The ‘V’ shapes contours

suggest that the contour

line is crossing a stream,

and the point of the ‘V’ is

Downhill/Uphill

Another relief feature that can help interpret the map are the hash lines found along special contour lines. These small markings represent a depression contour. Please refer to the following diagram to visually see the elevation change as a topographic map and as a raised relief map.

6. The direction of the hash lines depicts the change in elevation. Please explain how to interpret this map element.

Yet another way to view topography is as a profile. We can select a specific transect outdoors/on a map, and create a side view (think of a shadow of your face projected on a wall- showing your eyes, nose and chin). Match each map with the best profile.

7. Topo #1=____

8. Topo #2=____

9. Topo #3=____

10. Topo #4=____

11. Topo #5=____

12. Topo #6=____

So here is a sample profile taken from a topographic map. Notice that the map (on top) and the profile both depict distance, elevation and shape. The advantage of a profile is that it shows a view of the location as though you were standing there looking at it (versus from peering from above)

The following information from geology.edu might be of some use for an upcoming exercise:

Creating Topographic Profiles A very useful exercise for understanding what topographic maps represent is the construction of a 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. Not only does constructing a topographic profile aid in understanding topographic maps, it is very useful for geologists when analyzing numerous problems.

To construct a topographic profile, you must first decide on a line that is of interest to you. This could be an area where you want to go for a hike and want to know how steep to expect it to be, a line that shows the maximum relief (relief is the difference in elevation between the highest and lowest points) in the map area, or any other area in which you are interested. Once you have determined where you want to draw your profile, use the following guidelines to construct your profile.

First- Pencil the line of your interest in lightly on your map, this is the transect we want to make a profile of.

Second- Place a blank piece of paper along the line you have drawn. You may want to tape the paper to the map using drafting tape to keep them from moving relative to one another

Third- On both the blank paper and the map, mark clearly the starting and ending points of your line of section. Below these marks, write down the elevation of the starting and ending points of your section.

Fourth- Make a tic mark wherever the paper crosses a contour line on the map, making larger tics for the index contours and smaller tics for the intermediate contours. Write the elevation of the index contours below their tics on

your paper, you might want to start off writing the elevation of the intermediate contours as well to avoid confusion, but it will soon become tedious.

Topographic Map Exercise:

Please Work In Pairs—Do Not Write on Topographic Maps

Some of the most important information on a topographic map isn’t on the map itself, but on the Map Collar the area between the neatline and edge of the paper. Select a topographic map to answer the following questions.

Each topographic map, or quadrangle, is assigned a name. This name is found in the upperright corner in large print. What is the name for the map provided?

13. __________________________

Notice the small reference map in the lower right margin of the map. There you will find a small black box denoting the location of this quad. In what part of the state is the area located?

14. __________________________

What is the name of the map that adjoins the western edge of the quad?

15. __________________________

What is the name of the map that adjoins the southeastern edge of the quad?

16. __________________________

There is detailed information located on the bottom of topographic maps. When was the area first and last surveyed? Also, when was this particular map published?

17. First Surveyed (lower left corner) __________________________

18. Last Surveyed/Field Checked (lower left corner) __________________________

19. Published (lower right corner) _______________ (this date is printed… not a stamp)

Another useful piece of information in the map collar is the north arrow, which displays three separate north values. The line with the star represents geographic, or true, north. GN stands for grid north, which follows the UTM coordinate system, and MN stands for magnetic north which points toward the North Pole of Earth’s magnetic field.

What is the magnetic declination of the area shown on your map?

20. __________________________

Topographic Maps Continued

List the townships and ranges shown on the map.

21. Townships: __________________________

22. Ranges: __________________________

What are the section, township, and range at each of the following locations on the map?

23. Center of map: Sec.__________, T. _________, R. ________

24. Extreme northeast corner of the map: Sec._________, T. _________, R. ________

Lets complete a few activities using the latitude and longitude grid system on the map.

What is the highest elevation found on this map? What is the lowest?

25. Highest: __________________________ Lowest: __________________________

What are the latitudes of the southern edge and northern edge of the map?

26. Northern Edge: _______________________ 27. Southern Edge: ______________________

How many total minutes of latitude does the map cover?

28. __________________________

What are the longitudes of the eastern and western edge of the map?

29. Western Edge: __________________________

30. Eastern Edge: __________________________

How many total minutes of longitude does the map cover?

31. __________________________

The map is a ______ minute series topographic map because it covers ______ minutes of latitude and ______ minutes of longitude.

32. What is the overall shape of this map? Based on the series- why is it not a perfect square?

Name_________________________________

School________________________________

Google Earth Activity

For this portion of the lab, you will:

· Use Google earth to look at historical imagery

· Use the ‘measure tool’ within Google earth to measure the perimeter of a lake using the most current imagery and imagery from August 2002.

· Bring a printed screenshot of your map showing the change between the two images.

First- you need to either open, or download Google earth on a desktop or laptop (tablets and phones will not allow you to access the tools needed within this activity).

You will then search for Lake Piru, in the search bar of

Google Earth (top left corner)

You will then select the time-lapse button:

All imagery available for the area is now reviewable buy moving the drag button left to right- to a time desired. You will first select August 2002.

After selecting the ‘add a path’ tool- you will begin to trace the perimeter of the lake (where the water touches the land).

You can do this by individually clicking each spot (as I have done) or you can press down and drag. If you make a mistake, just click the Esc key to go back.

Once you are done- you can select the Measurement tab to see the

distance traveled (in meters and miles).

29. What was the perimeter of Lake Piru in August 2002 in both meters and miles?

____________________________________

The last part of this activity is to complete the same steps on the most current imagery provided by Google.

30. What was the perimeter of Lake Piru in the most current imagery in both meters and miles? When was this imagery taken?

____________________________________________________

What is the total difference in length measured? Has there been an increase or decrease of size?

31. _________________________________________________________________________________________________________

Patrich Physical Geography Lab | 1

Patrich Physical Geography Lab | 2

Patrich Physical Geography Lab | 2