The purpose of the exercise was to create maps for navigating at a nearby outdoor reserve, called the Priory (Figure 1). The exercise challenged us to think critically about what information would be best to put on our maps for the purpose of navigation. The maps will be used next week at the Priory to navigate to different checkpionts using our maps, a compass, and a GPS.
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| Figure 1: The Priory, shown by the red checkpoint, is 8 minutes away from the UW-Eau Claire campus. We will create maps to use for navigation at the Priory in the next field exercise. |
Background:
Navigating Essentials:
In order to navigate from one point to another, you need to know which direction you're going. There are multiple ways you can establish your direction. You could use the stars or sun to navigate. Most people use a compass or GPS to get from one place to another. This exercise focuses on maps, which uses a coordinate system for navigation.
Coordinate Systems:
Coordinate systems are mathematical models that transform the Earth's 3D surface into a 2D representation. There are two types of coordinate systems: geographic and projected. Geographic coordinate systems represents points on the earth using values of latitue and longitude, which are angular measurements of a point's distance from the center of the earth to the equator and prime meridian, respectively. Projected coordinate systems use latitude and longitude values along with mathematical equations to create different 2D representations (projections) of the earth.
Distortions are always created when coverting a 3D surface to a 2D model. Such distortions occur in shape, area, distance, and direction. Differnt projection preserve certain qualities and distort others. For example, the Mercator projection preserves direction and distorts area. This is why the Mercator projection is used for compass navigation.
Methods:
Two maps were created for navigation at the Priory. One map used the NAD83 (2011) UTM Zone 15N coordinate system along with the transverse mercator projection to display aerial imagery and 5 foot contours (Figure 2). The UTM coordinate system was used for one of our maps because UTM is commonly used for large-scale mapping. Zone 15 of UTM was chosen because the Priory fell within Zone 15 (Figure 3). Using a differnt zone would result in distortions of the map, and reduce the accuracy of the map. The transverse mercator projection was chosen for use with the UTM coordinate system because mercator maps have rhumb lines that are accurate for navigating terrain with a compass. The transverse orientation allows the UTM coordinate system to be split up into zones. (Zeiler, 2010).
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| Figure 2: This map of the Priory uses the NAD83 (2011) UTM Zone 15N coordinate system and transverse mercator projection. |
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| Figure 3: UTM zones in the United States. Retrieved from: http://www.wa6otp.com/utm.htm |
The other map used the geographic coordinate system WGS84 (World Geodetic System 1984), a popular geocentric datum (Figure 4). Geographic coordinate systems split the world up into a angular measurements of latitude and longitude based off angular measurements of a point's distance from the center of the earth to the equator and prime meridian, respectively (Figure 5). WGS84 was used for the second map because GPS's often use WGS84. This would make navigating the Priory easier. No projection was used with WGS84 because it would impede navigation with a GPS. The map included elevation data (red, yellow, and green shading), 5-foot contours, and aerial imagery of the priory.
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| Figure 4: This map of the Priory uses the WGS84 geographic coordinate system. |
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| Figure 5: Geographic coordinate systems, such as WGS84, devide the earth into angular units of latitude and longitude. Retrieved from: http://geoarc.blogspot.com/2013/02/coordinate-reference-systems.html |
Graticules were included on each map. The UTM map had graticlues labeled every 50m, and the WGS84 map had decimal degrees listed to 6 decimal places past the decimal point.
Aerial imagery and elevation data for both maps came from the City of Eau Claire. Data also came from a geodatabase created by our professor, Dr. Joseph Hupy. The geodatabase was called the Priory geodatabase, and included the 5ft contour feature class used for both maps. All data used in the lab was imported into a new geodatabase that we created.
One additional piece of information we included for our maps was our step count, which is the number of steps a person takes in a specified distance. After completing the step count twice, I determined my step count was 60 steps for every 100 meters. This knowledge will be helpful when navigating at the Priory next week.
Metadata for both maps can be seen below (Figure 6). The 5ft contours came from the Dr. Joe Hupy and the aerial imagery of the Priory came from the City of Eau Claire.
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| Figure 6: Metadata for both maps (UTM and WGS84) document where the data came from. |
Discussion:
The exercise challenged us to think critically about what information would be best to put of the map for the purpose of navigating at the Priory. We had to prepare maps that would allow us to plot coordiates (given by Dr. Hupy in the field) on our maps with reasonable accuracy, and allow us to accurately display the terrain. Displaying too much information on the map could actually be detrimental for navigational purposes. For example, we included 5 foot contours on our maps because they provided a balance between small (2 feet) contours that would crowd the map and large (10 foot) contours that would not be accurate enough.
Further more, we decided one map should have aerial imagery and the other should be a multi-colored digital elevation model. Elevation data would help make traversing the terrain easier, but having aerial imagery would also indicate helpful features in the terrain that a digital elevation model would hide. The WGS84 map had graticules labeled in decimal degrees to 6 decimal places past the decimal point. For the purposes of our maps, we would need to go at least three to four decimal places past the decimal to have accuracy at a large-scale map setting. We chose 6 decimal places past the decimal point because it provided an appropriate amount of accuracy.
For the UTM map, we used a graticule spacing of 50 meters because 50 meters is an appropriate distance to help keep track of how far you have gone in the field. Ten meter spacing would be too much detail, while 100 meter spacing might lead to our group going off the desired path while navigating to the next waypoint.
Of course, it was important to add essental map objects like a north arrow, scale bar, and relative fraction. The scale and relative fraction help convert distances on the map to distances in the real world. Knowing which was is north helps you travel in the right direction.
Conclusions:
The exercise helped build knowledge of coordinate systems, projections, and maps. I learned that it is important to critically think about what things benefit a map and take away from it based on its intended use. The created maps will come in handy for next week's exercise when our group navigates the Priory.
Works Cited:
Zeiler, Micheal and Murphy, Jonathan. Moedeling Our World. Redlands: Esri Press, 2010. Print.
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