Monday, November 13, 2017

Special Topics in GIS Lab 11

Using regression analysis in ArcGIS this week was eye opening. Prior to this week the analysis was all done in Excel and displayed in spreadsheets. This week we were able to pull the information into ArcGIS and perform the same analysis in a way that produced a visual representation as well as a summary of statistical reports that help the user analyse the testing. First you need the data for the analysis to be performed on. Then you simply use the Ordinary Least Squares tool in ArcGIS to set your data set, dependent, and independent variable(s) and let the program do the work. The results are provided in an easy to read report that gives all the information you need to decide if the results fit your analytical needs. This week in the lab we worked on interpreting the results. The focus was on the many values that the program calculates to analyse the regression. The tool that you run in ArcGIS even incorporated instructions int he results for reading the reported variables and determining if the result is what you are looking for.

The output of the OLS tool produces a residual map that visually shows the difference the actual data is from an expected value on the regression line. This visual aid can help us determine the accuracy and bias that could be present in the results. For instance if there is a pattern in the results or areas where the residuals are similar in a certain area it could show a bias or non-random correlation. This information is good to have because it could clue you into the fact that you need to use another variable to run the regression analysis.

Finally at the end of the lab (of course) it was revealed that rather than running the tool many times on different independent variables you can simply run another tool that includes all of the variables you wish to analyse and reports the most accurate result possible. The capability of technology today is impressive and makes me wonder what the engineers and analysts will have the software calculating for us next!

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