# Differences and Similarities Between Mean Local Relief and Slope

#### Summary

In this lab students investigate the effect of raster scale on calculations of mean local relief and slope. Students learn about the differences and similarities between mean local relief and slope, and how to create their own functions using Python.

Used this activity? Share your experiences and modifications

## Context

#### Audience

This exercise is used in an introductory GIS course for geology and environmental studies students.

#### Skills and concepts that students must have mastered

Familiarity with ArcMap and ArcCatalog;; basic geoprocessing; basic familiarity with Python scripting; projecting a dataset

#### How the activity is situated in the course

This is the fourth in a series of stand-alone GIS exercises that introduce students to using Python Scripting for ArcGIS.

## Goals

#### Content/concepts goals for this activity

Using raster calculator and map algebra; creating and using functions in with Python; the effect of scale on raster calculations; exporting raster data as a spreadsheet.

#### Higher order thinking skills goals for this activity

Testing hypothesis with GIS; reusing code in computer scripts.

## Description and Teaching Materials

Digital Elevation models are available for the entire world and at a variety of scales. Elevation data has the power to tell us lots of things about the landscape and its history. However, landscapes are very complex and DEMs at lower resolutions can hide important things about the landscape. The HydroSHEDS project provides DEMs covering the entire world at a variety of resolutions, allowing students to compare how different scales effect DEMs and raster calculations.

Lab 6a: In this homework exercise students read a paper on tectonic geomophology and and download DEM data from HydroSHEDS for the area around Wenchuan, China.

Lab 6b: In this lab exercise, students clip and project their DEMs to prepare them for analysis. They then create integer slope rasters for each DEM scale. Students then export histogram information as a table and compare histograms for each slope raster. Finally, students learn about functions, and look at examples of functions in Python scripts.

Lab 6c: In this lab exercise, students write a function to calculate mean local relief from a DEM. Students then run their function in the Python interpreter for each of their DEMs.

Lab 6d: In this lab exercise, students create histograms from their mean local relief rasters, and create a map which includes a comparison of their histograms.
Lab 6a: Data Download for Rasters Lab (Acrobat (PDF) 418kB Jun12 17)
Lab 6b: Raster Calculations (Acrobat (PDF) 437kB Jun1 17)
Lab 6c: Mean Local Relief (Acrobat (PDF) 187kB Jun1 17)
Lab 6d: The Effect of Scale on Mean Local Relief and Slope (Acrobat (PDF) 115kB Jun1 17)

## Teaching Notes and Tips

Lab 6b references python scripts used in previous exercises in this class, which are available on SERC. However, if using this exercise on its own, you will want to substitute the referenced scripts for examples on your own, This should have no detriment to the experience of the students.

Although we belief the Python exercises to be clear, students should be given an opportunity to do the Python component, Lab 6c in an environment where a teacher or T.A. will be available to over one on one help to assist students with any conceptual issues they are having.

## Assessment

Students are assessed on the clarity and professionalism of their map, if it effectively conveys the effect of scale on mean local relief and slope. They are also assessed by a workflow and letter summarizing what they did and learned in the lab.

## References and Resources

The analysis tests an assertion in the following paper, which should be read for context: Montgomery, D. R., & Brandon, M. T. (2002). Topographic controls on erosion rates in tectonically active mountain ranges. Earth and Planetary Science Letters, 201(3), 481-489.