Accuracy, Precision, and Topographic Data
In this field/lab exercise, geomorphology students collect topographic data about a small landform using three different methods and critically compare their accuracy and precision. Students produce three topographic maps and write a short report describing their results and analysis.
- how to use three different tools (methods) to collect quantitative position data about a landscape: a level and tape; a GPS (global positioning system); and a total station.
- how to compile these data on a spreadsheet, and then plot them as a topographic map or surface using computer software.
- how to evaluate the quality (accuracy and precision) of those data by comparing the two maps to what you know is actually out there.
- finally, give an assessment of the benefits and limitations of each method for collecting data.
Methods of GeoscienceWe believe that students must understand the sources and limitations of the spatial measurements used in studying Earth's surface. This exercise challenges students to think critically about precision and accuracy of x,y,z data. They are typically stunned to learn that 50 site-level points makes a better map than 500 GPS points. Thus, this exercise addresses misconceptions common among novice geoscientists ("technology always provides the best data" and "more data is always better").
Context for Use
Description and Teaching Materials
- Student Handout for Geomorphology Exercise: Accuracy, Precision and Topographic Data (Microsoft Word 87kB May7 12)
- Grading Rubric for Topo Accuracy Exercise (Microsoft Word 27kB May7 12)
Teaching Notes and Tips
After division into MAP teams and re-organizing into expert groups, I start the exercise by marching all of the students to the site and ask them to make a sketch of what the topographic lines for this feature should look like. Then they break into expert groups, which is each accompanied by an instructor (GPS) or TA (site level and tape) or tech (Total Station).
The sequence typically plays out like this:
- after a brief introduction to saving waypoints, the GPS group members each take 200-400 position measurements and are triumphant as the head to the computer lab to download their data.
- the site level group breaks into teams and discusses how to use these tools (site level, stadia rod and tape) to locate x,y,z coordinates in a local framework. The TA must check their proposed method to ensure that they are recording sufficient data to reconstruct their positions. They typically can college ~50-60 positions.
- the total station group finds set up excruciatingly slow (they are often still setting up when the GPS people are headed back with data). Once set up, they typically collect 25-35 points.