Geospatial Field Methods: Terrain Creation and Survey

Introduction:

We were tasked to create a landscape within a 1.26m x 1.19m wooden frame featuring: a plain, a mountain, a ridge, a valley, and a depression. After forming our landscape, we were to survey the surface of the landscape for future mapping purposes. We were to form our landscape on the sandy point bar of the Chippewa River underneath the UW-EC campus footbridge.

Methods:

Before shaping the terrain, we leveled the ground surface underneath the survey frame, in order to standardize the elevations for our survey. After the frame was leveled, we created a hill along the left side of the frame, a valley running from the top left to the bottom right, a ridge running parallel to the valley, a depression in the top right corner, and a plain in the lower left corner (Figures 4-5). Next, we put scotch tape over the edges of the frame and marked them with a pen at 10cm intervals from a point of origin on the inside edge of “1D” on the frame (Figures 1-3). The boards themselves were all the same length, but due to the frame’s design, the X-axis (from 1D to 1B) was 1.26m long, and the Y-axis (from 1D to 1C) was 1.19m long. We made a grid with a sampling interval of 1dm, making a 12 x 11 grid with 132 total points. We started our survey at (1,1) which we found by placing modifiable string gridlines 10cm from the origin point of the X and Y-axes. After the gridlines were in place and pulled taut, we recorded the distance from the gridlines to the ground surface using a meter stick and recorded them in centimeters to 1mm accuracy (Figures 6-8). We recorded the distances from the grid to the ground as Z-values in a Google drive spreadsheet. After scanning point (1,1,19.8), we scanned (1,2,19.8) and continued working our way up the Y-axis until reaching the top of the frame, at which point we moved to (2,1,19.3) and followed the same procedure. We continued in this fashion until the survey was completed. We decided to use the base of the boards as our sea level. The boards of the frame measured 18.1cm tall, so I created a calculated column in Excel to subtract the distance between the gridline and the ground from the frame height. This made a new column with the height above or below sea level.

Discussion/Conclusion:

Leveling the frame was incredibly helpful, as it allowed us to record the actual slope of the pre-existing plain, and the landscape as a whole. Choosing the base of the frame as “sea level” wasn’t the best practice as most of the plain and other features are below “sea level”. Measuring the distance below the gridlines allowed most areas to be measured with ease, as none of our features surpassed the frame height. The only area that caused difficulties was the middle of the frame between (5,5) and (8,7), as they caused a lot of movement in the arm of our ruler holder as he was surpassing the comfortable range of his reach. This area was also more difficult to survey because the distance from the ruler caused some issues with properly sighting the distances between the ruler and the gridlines. Upon conducting a little research into sampling methods, I learned that my group conducted our survey using “systematic sampling” and that this sampling method may have caused us to under-sample some areas and features that fell between the gridlines. To compensate for this under-sampling, we should have instead used the “stratified random sampling” method. In order to have used “stratified random sampling” we would have created a grid system, and sampled one random point from within each individual square of the grid, rather than just from their verticies.