An interesting question came about a few days ago. While I have been discussing ESRI’s geoprocessor and how one can use it effectively, I failed to define what geoprocessing is,, either within the ESRI realm or the general GIS realm. In short, geoprocessing is an operation performed on geographic (spatial) data. In other words, it is when one uses data to perform some operations and receiving results. An example would be geocoding. The user provides spatial data (an address), which we geoprocess to identify the output (latitude and longitude). In the ArcGIS world, there are a few methods for geoprocessing: running commands from the ArcToolbox, the Model Builder, the command line and Python scripting (the one I focus on mostly in this blog).
The ArcToolbox
The ArcToolbox of ArcGIS 9.3
The ArcToolbox is a collection of tools provided by ESRI that achieve a number of geoprocessing operations. They are logically organized in themes based on the functionality, and are available to use without any customization. These operations can be very powerful and achieve great results. As you can see from the image on the right, there is a number of tools available to you to use. Depending on the extensions you have installed, you will see some different results, but the Geocoding Tools we mentioned above are available with any kind of license. To use any of these geoprocessing tools, you simply double-click on its name, and a window will pop up asking you for the required inputs and outputs. Pay attention to all the options available to you, and make use of the help button to clarify what the operation does, and how it is achieved.
The Model Builder
The Model Builder Window
The Model Builder is a wonderful program written by ESRI that allows you to graphically define geoprocessing operations. Using a simple tool, a user can drag and drop operations and data on a canvas, and connect them with directional arrows (signifying direction of data). On the example on the right, we follow the Address Geocoding operation. There are three data inputs for the operation, including an address locator, address fields to be used, and finally the input table with the addresses. There is one more data element in the picture, the output feature, on the far right. Note that all data are represented by ovals. The operation, which is in the middle, receives data from all the arrows pointing to it, and returns data to the arrow pointing outwards. Notice that the operation is in a rectangular box rather than an oval, to distinguish it.
The Command Line
The Command Line Window
The command line window is one more way to achieve geoprocessing when one is using ArcGIS. The window simply allows one to type commands, an hit enter to execute them. Some users are more familiar with this interface, and like the speed of which you can type operations. Typing a few letters in the top box will give you a list of all commands starting with those letters. Pressing space will bring the tooltip shown in the top of the image on your right. As you can see, it tells you what the tool expects to run. In this case, it expects an input table (in_table), an address locator (address_locator), the address fields (in_address_fields) and where to save the output (output_feature). Optionally, you can set the out_relation_type (notice the curly braces this time).
Python Scripting
Python Scripting Geocoding
The perhaps most complex way to perform geocoding is done through Python scripting. The example on the right actually presents geoprocessing code. What happens when one uses Python Scripting to create geoprocessing operations is similar with the command line option talked about earlier, with some slight changes. Python scripting gives you the option to interact with the data deeper. What this means is that the user can now access an individual point by latitude and longitude. And since all vector spatial data are built from points, this means you have deep access to any spatial data using Python (to see more about Accessing Geometries using the Geoprocessor click here). Also, as Python is a general use scripting language, you can find reusable code by other users (in the form of modules) to achieve things like reading Excel files (click here for an overview).
And that is what geoprocessing is. Operations that work on spatial data. In the ArcGIS realm, that means either using ArcToolbox, the Model Builder, the Command Line interface or creating your own Python Scripts to achieve your desired results.
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