Ask A Cartographer

Help Needed with Spatial Statistics Tools in ArcGIS / 911 Calls - Hot Spot Analysis

November 05 2010 | 1 comment
Categories: Map Data

I recently started working with some of the Spatial Statistics tools found in ArcGIS, namely Collect Events with Rendering, Hot Spot Analysis with Rendering, and Z Score Rendering. In fact, I am essentially trying to recreate the file found here:

When looking at the Adobe .pdf file found in the link, I cannot figure out two parts in particular:

1) I am able to easily apply either graduated symbols or Z-scores to a given shapefile but I cannot figure out how to display both graduated symbols and Z-scores simultaneously as found in Figure 4 of the file. I can display one or the other just fine, but I cannot figure out how to represent both. I have experimented with "Multiple Attributes" in the shapefile's symbology settings but I cannot figure out the correct combination to use.

2) I am also having trouble figuring out how to duplicate Figure 7, i.e. a raster surface created from the graduated symbol vector shapefile found in Figure 4. The file recommends using the IDW tool; I have tried using it but my results look nothing like those found in Figure 7. Of course, given I cannot figure out how to properly recreate the effects found in Figure 4 it stands to reason I may therefore be unable to successfully recreate Figure 7, as well.

If any of you can offer me advice or instruction on how to effectively duplicate this file I appreciate your guidance. In fact, without being too presumptuous a step-by-step tutorial would be ideal. Please explain parameters used for certain tools, particularly the IDW tool (e.g., Power, Fixed versus Variable Distance, cell size, etc.).

Best Regards,

Mapping Center Answer:

Since I didn't actually create those maps, all I can provide is the quick and dirty answer to your questions:

1) Regarding combining z-score and graduated circle rendering: Render your results using the z-scores (this will give you the right colors, but the circles will all be the same size). Next, right click on the layer in the Table of Contents (TOC) and select the Symbology tab. There you can change the size of each circle separately (just click on the circle you want to change).

2) Regarding the raster surface: The surface was created from the z-score points using the IDW tool in Spatial Analyst (the output feature class from the Hot Spot tool has a field with the z-score values - use those to create the raster surface). Once you get the z-score surface using the IDW tool, right click on the new surface layer in the TOC and click on the symbology tab. There you can find the hot to cold color ramp (you may have to invert the colors so cold/blue is the negative values and hot/red is the positive values). Use the "stretched" option … it looks nicer. Then on the display tab, you can play with the transparency.

Not Enough Information - Please Provide More Instr posted by Jonas Baughman on Nov 10 2010 7:45PM
Thank you for your answer, although I must be honest and admit it did not answer my questions to my satisfaction, particularly the part about the IDW tool.

I already know the basics of how to use the IDW tool to receive an output raster, but I need detailed instruction on how to apply various settings within the IDW tool itself. As I mentioned in my initial question, I need specific guidance on various settings/options within the IDW tool such as Distance Bands, cell size, Power, Fixed versus Variable Distance, and so on.

Again referencing the 911 Calls for Service .pdf file mentioned previously, the file simply states to use the IDW tool but it offers no specific instruction on HOW the IDW tool was used to achieve the end result (i.e., the blue and red colored raster). This is where I request further guidance from you.

If you would like to post a comment, please login.

Contact Us | Legal | Privacy |