SWARS Spatial Analysis, The Book (6)

*Go to ArcGIS Desktop Help, read as much as you can find about Spatial Analyst and Raster Analysis Environment Settings.

Turn on the Spatial Analyst

First thing first! For this SWARS analysis, the most important group of ArcGIS functions is in the Spatial Analyst Extension. So, make sure you even have that extension!

To get the ArcMap Spatial Analyst toolbar out, if you have the extension installed and licensed:

1. in ArcMap, click the menu button
2. select
3. in the Extensions dialog, check on the Spatial Analyst extension
4. then, click the menu button
5. select
6. check the Spatial Analyst option


You should now see the Spatial Analyst toolbar on your main ArcMap interface.

If you don't see the Spatial Analyst option, that means you don't have that extension for your ArcGIS. You will need some extra help getting it solved.


Now, here are a few very important concepts which we will apply but you might not have paid enough attention to before.

* Analysis Mask
* Analysis Extent
* Snap Raster
* Cell Size


Ding! Ding! Ding! Any bell rings?? If not, you should and can find all the explanations you need in ArcGIS Desktop Help. Just go into the Help and type in those key words to find them. I will explain a bit more when we get to them.

Get familiar with these key concepts first. It's worth the time!!


**ArcGIS Desktop Help is your first and perhaps one of the best places to go for information on how to use ArcGIS! Get used to it!


Now you should see the Spatial Analyst toolbar on your main ArcMap interface. Click on menu, then in the drop-down list, click .

The raster analysis Environment Settings dialog box will appear as shown here.

This is where you do it once and save a whole lot of time later.

As I said during the Hawaii SWARS Workshop, ideally, we would have a boundary polygon (Analysis Mask) that encompasses precisely all and only the areas we will be analyzing, which itself is so well defined within such a "snuggy" rectangle (Analysis Extent)! Should such a national treasure exist, all shall be easy. We can just use it for all our raster analysis environment settings.

Unfortunately, many of us don't score that lottery. Therefore, we are likely required to "create" it! This is where it gets interesting and creativity shall shine.

Case Example

For our Palau exercise, we will:

* limit our Analysis Extent to the Babeldabo island;
o you want the Analysis Extent to be as small as possible;
* snap all rasters to the existing DEM grid; and
o use one of your existing rasters as the snap raster;
* set our output raster cell size to the same as the DEM grid, 10 by 10 meters.
o 10 by 10 feels about right for the size of most of the islands.

Again, it's up to you to determine exactly how to set those parameters!