Lab 1: Creation of a Digital Elevation Surface Using Critical Thinking Skills and Improvised Survey Techniques

Intro
o Define what sampling means, with a strong focus/emphasis on what it means to sample in a spatial perspective.
Sampling involves gathering a small fraction of data in order to represent a whole population. This is necessary a lot of times because rarely does one have the time, energy, money, equipment, ability, etc to conduct a sample of an entire population/sampling frame.  An appropriate sampling technique is essential therefore to obtain a representative and statistically valid sample of the whole.  In a spatial sense, this means allowing enough data to create a stronger representation of the area.
o List out the various sampling techniques
- Random sampling (point, line, area)
- Systematic Sampling (point, line, area)
- Stratified sampling (systematic, random)
- Cluster sampling
- Multistage sampling
o What is the lab objective(s)
The objective of this lab is to think geospatially by constructing an elevation surface of a terrain which is contained within a square meter sandbox.  One is to create a Ridge, Hill, Depression, Valley and Plain out of the sand (figure one below shows the topography of the sandbox).

Figure 1 - Feature's carved out in group two's sandbox

Once these features are established, the group will be able to map out the elevated surface using the original survey technique.
   

Methods
o What is the sampling technique you chose to use? Why? What other methods is this similar to and why did you not use them?

Our group used the systematic sampling technique in order to establish the most data point to capture the majority of the grid, this we felt was the most accurate method for this particular task, unlike the other sampling methods.
 o List out the location of your sample plot. Be as specific as possible going from general to specific. 
The sandbox was located at University of Wisconsin Eau Claire's campus, east of Phillip's hall and across the road from Roosevelt Ave.  It was approximately 30 meters from the loading dock, being the sandbox sandwiched between two others.
o What are the materials you are using?
Our group utilized a meter stick, tacks and strings to produce the most accurate grid.
o How did you set up your sampling scheme? Spacing?
Our group had a total of 23 points on the Y-axis and 23 on the X-axis, each point being measured out in 5 cm intervals shown in figure 2 below.

Figure 2 - Displaying grid with X and Y axis

o How did you address your zero elevation (sea level)?
Our group made the sea level elevation be the lowest point of the digital elevation model.
o How was the data entered/recorded? Why did you choose this data entry method?
A three value table was established with x and y values as well as the associated elevation for each point (Z).  Z was recorded by measuring the distance from the string to the sand every 5cm interval. One member measured each point as another wrote down the measurements in a notepad to speed up the process.  After all the recordings were made, it was entered into an excel spreadsheet.

Results/Discussion:
o What was the resulting number of sample points you recorded?

A grand total of 576 sample points were recorded.
o Discuss the sample values? What was the minimum value, the maximum, the mean, standard deviation, etc.
The minimum value was 4.5 cm, and the max was 19.6 cm.  The mean was 12.81 cm and the standard deviation was 2.81.
o Did the sampling relate to the method you chose, or could have another method met your objective better?
The systematic sampling method seemed to work out quite nicely, using random samples for this particular exercise would have made little sense, systematic was therefore the most obvious choice.
 o Did your sampling technique change over the survey, or did your group stick to the original plan. How does this relate to your resulting data set?
Our group stuck to the original plan throughout the process, as the measuring process worked out quite smoothly and efficiently.
o What problems were encountered during the sampling, and how were those problems overcome?   The one issue our group had was occasionally losing track of the amount of measurements made per each row.  This was simply resolved by remeasuring that particular row.   

Conclusion:
o How does your sampling relate to the definition of sampling and the sampling methods out there.

Our goal was to gather enough data to accurately portray the elevation changes throughout different areas of our sandbox, it therefore had to be systematic by nature.  
o Why use sampling in spatial situation?

Often times there is too big of an area to measure as a whole.  Therefore, a statistically valid sample/representative of the whole is necessary.
o How does this activity relate to sampling spatial data over larger areas?
Despite this being a pretty small sample site, similar sampling methods could be applied to larger study areas using the same grid technique.
o Using the numbers you gathered, did your survey perform an adequate job of sampling the area you were tasked to sample? How might you refine your survey to accommodate the sampling density desired?
It's apparent that the numbers display elevation changes throughout the sandbox fairly well.  Looking back, it may have been better to have added more plot points to refine the accuracy, but our time was limited.

References:

http://www.rgs.org/OurWork/Schools/Fieldwork+and+local+learning/Fieldwork+techniques/Sampling+techniques.htm