This activity was to serve as an introduction as to how to go about creating a coordinate system and to evaluate a digital elevation surface. In order to do this it was required to include a linear peak, valley, hill, depression, and a plain. In the real world digital elevation models are used in ways ranging from ecologists estimating wildlife distribution to natural disaster specialist to see the impacts of that disaster (NOAA). Bamber and Gomez-Dans (2005) assed two different methods to analyze the accuracy of the digital elevaion model of Antarctica. Reading through this article shows how intricate these digital models must be and how critical thinking and problem solving plays a huge role in determining the accuracy of digital elevation models. Our task was much simpler and on a much smaller scale, of course, but none the less to think spatially and problem solve.
Study Area
- Date: 18 September 2015 from 1:30-4pm
- Sandy bank of the Chippewea River Valley
- Conditions: Overcast, Average temp. 60.7°F (retrieved from Weather Underground)
Methods
In the sandy bank of the Chippewa River a 122cm by 125cm hollow rectangle was placed and leveled. To level the box we placed a level on each corner of the rectangle. We decided we would fill sand up to the bottom edge of the rectangle. To level the sand we placed a level on top of a meter stick placed in the center of the rectangle. We measured the levelness along the x-axis and y-axis.
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| Figure 1. Students Casey Aumann and Ally Hillstrom building the features. |
Construction of features
Once the sample was leveled and ready to go, the features were constructed. A linear peak, plain, depression, valley, and two hills were shaped from sand as well.
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| Figure 2. The final constructed features. |
Linear peak: A ridge with a high point that continues
Hill: A peak with an isolated high point with a rounded top
Depression: The opposite of a hill, where there is a low point
Valley: An elongated lowland channel
Plain: A flat expanse of roughly the same elevation
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| Figure 3. The coordinate system 8 x 8cm squares. |
Making the Coordinate System
First, we placed push pins every 8cm around the frame of the rectangle. String was wrapped around the pins to make 8 x 8cm squares within the rectangle.
Second, the coordinate system was labeled using numbers along an x and y axis. For example, the squares were labeled X1, Y1; X1, Y2 and so on.
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| Figure 4. Casey measuring the z-values and Ally entering the data. |
Data Collection
All measurements were taken from the upper right-hand corner of each square using a meter stick.
This coordinate system produced 210 points and the measurements were recorded directly into an excel spreadsheet (shown to the left).
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| Figure 5. Data in excel. |
The z values are negative because the top edge of the rectangle was assigned sea level. When transferring the data into ArcGIS we will multiply all of the z values by -1 in order to create positive values.
Discussion
This activity allowed us to get our hands dirty and experience the challenges of creating a coordinate system and trying to establish a digital elevation surface.The challenges we came across ranged from choosing where sea level should be to selecting the best spot to represent the whole square in terms of elevation. Sea level was set at the bottom edge of the rectangle because then all of the measurements would be negative, and it would make measuring the features in the middle of the rectangle easier. For example, it would be difficult to get an accurate measurement of the middle of a linear peak without destroying the feature. It would be interesting to see how this is achieved successfully using different methodology. Another problem that occurred was with choosing how big to make the squares within the rectangle. Eight by eight squares were chosen because they were small enough to ensure a representative survey of the features within the rectangle. However, there were sections of the rectangle we disregarded in order to have a perfect square because we did not know how to correctly record a value from less than a whole square. While recording the z values some error could have occured because two students took turns measuring. Also, the values could have varied a bit because the meter stick could have gone into the sand instead of representing the surface of the feature. The conditions allowed us to work without problem, with that said it took a substantial amount of time to work through the difficulties mentioned above and then to measure all 210 points.
Conclusion
In conclusion the difficulties we experienced helped us develop our critical thinking skills and our ability to think spatially. This activity taught us that developing and evaluating a digital elevation surface takes a great amount of time and serious consideration of the available tools. It was a great starting point to introduce this topic and to introduce us to thinking spatially.
References
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