Hot Spot / Point Density Analysis: Kernel Smoothing Revised by Carolyn Talmadge on January 15, 2016 SETTING UP... 1 ENABLING THE SPATIAL ANALYST EXTENSION... 1 SET UP YOUR ANALYSIS OPTIONS IN ENVIRONMENTS... 2 CONDUCTING THE ANALYSIS... 2 PERFORMING CHANGE DETECTION ANALYSIS... 4 MAKE YOUR RASTERS PERMANENT... 5 Setting Up 1. If needed, map the S drive: a. Go to Start Computer. b. From the menu bar at top, select Map Network Drive. c. Map Network drive S to \\rstore2\gisprojects$. 2. Start Arc Map and open the UgandaConflict.mxd from S:\classes\DHP_P207\Hot_Spot_Analysis\ (or alternatively, download the data from our website). 3. Create a folder in your H: drive called Hot_Spot_Analysis 4. Once open, immediately save the.mxd file to your Hot_Spot_Analysis folder in your H drive. 5. Take a moment and look at the data. The data were acquired from the following sources: a. Conflict Data: ACLED - Armed Conflict Location and Event Dataset b. Geographic Boundary Data: GADM - Global Administrative Areas Database 6. Question: What is the coordinate system and linear units of the data frame? Does it match the spatial reference for the data layers? Enabling Spatial Analyst Extension 1. From the menu bar select Customize Extensions and check the Spatial Analyst check box. Now you can use the Spatial Analyst functionality (you must do this every time you use this tool at a new computer). 2. From the menu bar select Customize Toolbars Spatial Analyst. 1
3. You should now have the Spatial Analyst Toolbar loaded. Set up Your Analysis Options in Environments 1. From the Geoprocessing dropdown menus select Environments. 2. Under Output Coordinates Output Coordinate System select Same as Display. We do this so that any new layers generated are in the same projection as the coordinate system. 3. Under Processing Extent, set Extent to Same as Layer UGA_adm3_proj. This defines the geographic extent of the raster datasets you create during your analysis. We set the extent so that the new raster covers Uganda completely. 4. Under Raster Analysis and set the mask to UGA_adm3_proj. This clips the new raster to the shape of Uganda. 5. Press Ok. Conducting the Analysis 1. Turn on the Conflict 2000 to 2004 point layer. 2. Open ArcToolbox. In ArcToolbox, select Spatial Analyst Tools Density Kernel Density. This brings up the Kernel Density window. 3. Enter the values above for the various parameters Keep the default location of Output Raster. 4. Question: What units are the search radius and output cell size in? 2
5. When complete click OK. 6. A new raster layer should appear in your Table of Contents. 7. Change the color scheme of the raster layer to a hazard color model, shown below. 8. Examine your new data layer. How well does it represent your point data? 9. Now rerun the density surface a couple more times and try different values for the search radius but keeping the output cell size 1000. 10. Question: What search radius is best? 11. After we determine the best search radius as a class, run the density tool once again on the Conflict 2000 to 2004 layer. Once created, change the name of this new layer in the table of contents to Density2000_2004. 12. Now, run the density tool on Conflict 2005 to 2010 with the same search radius and cell size we used for the Conflict 2000 to 2004. Change the color model of this new layer to hazard color scheme and change the name to Density2005_2010. 13. You should now have two raster density surfaces in your project. Remove any extra densities layers you made. 14. Compare the two different time period density surfaces? Do you notice any differences? 15. Save your project. Performing Change Detection Analysis 1. While visual comparison is helpful, we want to quantify the change over time by subtracting one density surface from the other. 3
2. We want to create a new raster layer that is the results of subtracting the 2000-2004 density layer from the 2005-2010 density layer. 3. In ArcToolbox, navigate to Spatial Analyst Tools Map Algebra Raster Calculator. This brings up the Raster Calculator Window. 4. Build the expression "Density2005_2010" - "Density2000_2005". Double click on the layers to add them to the expression box. (Using the Raster Calculator Keypad is helpful. It reduces the chance of syntax errors.) 5. When complete click OK. 6. A new raster layer should appear in your table of contents. 7. Symbolize this new raster using a standard deviation classification with 1 standard deviation and choose a diverging color scheme. 8. Examine your results. 9. Make a thematic map depicting significant increase and significant decrease of conflict from the two time periods. 4
Make Your Rasters Permanent Currently your rasters only exist in temp space located on the local drive. You need to save them in your H drive in order to reuse them. 1. Right click on each of your raster density surface layers, select Data Export Data. 2. Save each to your project folder with the appropriate titles (remember, rasters must contain no more than 8 characters and do NOT put a space in the name). 5