Sandbox Survey I: Understanding Coordinates and Grids

Introduction
Sampling is a method of investigation of a large area (or population) by gathering data from a small portion of the whole to make estimates about the whole. Spatial sampling techniques involve 3 types: Random, Systematic, and Stratified.

1. Random sampling is the least biased, however it is also the least reliable in terms of representation, because it is hard to know if the points are evenly distributed and/or hit each big area. 
2. Systematic sampling is where there is a planned pattern of which data points will be collected. It is more reliable than random sampling but has potential to be more biased. S
3. Stratified sampling is where the larger group is divided into subsets and then data points are systematically gathered.

Each technique can be used with points, lines, or area. The objective of this lab was to perform a terrain analysis utilizing one of the three sampling techniques mentioned above as well as an established coordinate system.
Methods

• Technique: The sampling technique used in this project is stratified sampling. This method was chosen because it allowed for more data points to be collected where necessary. It also allowed for the whole area to be broken up and appropriately analyzed. It is similar to the systematic sampling because there was a pattern used. In the bottom half of the sandbox, the there was not a lot of changing terrain so every other point was collected in alternating rows. Systematic sampling was not used because it does not allow for collecting more points in certain subsets the way stratified sampling does.
• Location: The sample plot is located in Eau Claire, Wisconsin on the UWEC campus. More specifically, in a sandbox by the biology shed to the left of Phillips Science Hall. 
• Materials: The materials used were: sandbox plot, sand, snow, tacks, string, meter stick, pen, and paper.
• Setup: The plot was 114 cm x 114 cm, so it was divided into a grid of 19x19 (each square being 6 cm by 6 cm) using tacks, string, and meter stick.
• Zero elevation: sea level was determined to be level with the sandbox because it is solid and cannot be moved with the weather as the sand/snow could.
• Data collection and  entry: due to cold weather, it was not feasible to enter data into a computer as it was collected. Data was handwritten into a pre-made data table and later entered into Microsoft Excel to be shared and stored. X, y, and z planes were measured using the meter stick and rounded to the nearest 1/2 centimeter. 

Figure 1. Collecting data points with the meter stick

Figure 2. The sandbox plot with coordinate grid including a ridge, hill, depression, valley, and plain.

Results and Discussion
A total of 213 data points were recorded. The minimum value for depth was -8cm, and the maximum value was +5cm. The mean depth was -2.7cm. The sampling method seemed to work well and ample data points were collected. However, systematic sampling could have provided for less risk of bias. The sampling method was decided before data collection began and was not changed throughout, however, as terrain became more diverse on the north end of the plot, it was decided that it was necessary to begin collecting more data points to accurately account for more drastic elevation changes. A few problems that were encountered were loose strings resulting in slightly uneven grid squares, but these were easily fixed by tightening the strings and adjusting the tacks holding them in place.

Conclusion
The technique used in this project demonstrates the definition of sampling because points from smaller areas were collected in order to make assumptions about the larger area. Sampling is an ideal strategy in spatial situations because it saves time (not having to collect every single data point) and money, from a business perspective. When cartographers and GIS technicians are collecting data to create maps, it would take far too long and be quite unnecessary to collect every inch of elevation and data. For example, to put the Chippewa River on a map, it would be excess work to record the depth of the river at every 4 inches. It would make more sense to use a sampling technique to get adequate data and make reasonable assumptions about the gaps. The survey done on this sandbox plot provided an adequate amount of data to make safe assumptions about the terrain. To refine this survey, however, the systematic sampling strategy might be more adequate because it eliminates all bias while still keeping a decent representation of the larger area.

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