Building Models and Geoprocessing in ArcPy

A- Model Builder In Arc GIS Pro

Below is a model that was built in Arc GIS Pro, specifically for soil types and farmland. The goal of the model is to remove land from basin areas that is not the best suitable land for farming. Therefore, the basins that are left are the most suitable "prime" farmland to grow crops which is shown in purple below. 

Before we go any further, what is a model? what is a model in Arc Pro?

This definition above is pretty straightforward according to Wikipedia...

ModelBuilder is a visual programming language for building geoprocessing workflows. Geoprocessing models automate and document your spatial analysis and data management processes. You create and modify geoprocessing models in ModelBuilder, where a model is represented as a diagram that chains together sequences of processes and geoprocessing tools, using the output of one process as the input to another process. - Esri

Example from Esri's Website

 

https://pro.arcgis.com/en/pro-app/latest/help/analysis/geoprocessing/modelbuilder/what-is-modelbuilder-.htm

So now that we know what a model is, and what it looks like in Arc GIS Pro, Let's get to it! 

To begin working with this  model, we need to open up Arc GIS Pro. 

• Go to the Analysis Tab in your Project
  
• Click Model Builder
• Give your model a name and save it
• Now we can start Geoprocessing!
• Add data into your model, these will appear as variables or blue circles
• Search the analysis toolbar for ArcPy Tools and Scripts, and drag them into your model
• Define your output data
• Pull In any iterators, other variables, preconditions, and or logic variables needed
• Run your model
• See Your Results!

Sounds Pretty Easy Right? 

Well it's not until you get used to it...

For this model, we selected the input data in the Arc Pro Project

We ran the Clip Analysis tool, and imported the soils data and the basin data to do this. Then we selected the soils clipped to the basin area that were not prime farmland based on a field in the attribute table using a query expression. Then we ran the erase tool to remove these areas from our original basin layer. As you can see there are 3 tools, 2 input data variables, and 3 output data variables with one expression query in the select tool. You can see the model below saved in my project's toolbox. 

 You can also export models out as python files so they can be standalone scripts! 

B- Geoprocessing with Python Scripting: ArcPy

Below is a flow chart for building a custom python script in ArcPy.  This Python script takes a shapefile of hospitals, adds XY coordinates or LAT/Long's to the points, then establishes a buffer of 1000 meters around the hospitals, and the dissolves the buffer to make sure lines do not overlap the buffered area around the hospitals.

Each step is logged in the terminal with the script's start time, end time, and the tool's name that is running at that point in time.

Steps that my flow chart above explains in full detail:

1        XY Coordinates – In order to add X and UY coordinates to the hospitals shapefile, I wanted to copy the file first using the arcpy.Copy_management tool to create my new shapefile. I then ran the AddXY_management tool to get the coordinates added to the attribute table for my hospitals.

 https://pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/add-xy-coordinates.htm

2        Buffering – The buffer analysis was tricky with setting the units of measurement. I needed to run the arcpy.analysis.Buffer and I input my hospitals XY shapefile, then set the new shapefile’s name that I was creating (hosXY_buffer, and then I sett ;the buffer to “1000 Meters”. This was trial and error because originally, I left the 3rd argument as 1000 which defaulted to U.S. Feet since the hospitals shapefile is in a spatial reference of a state plane coordinate system that is in U.S. Feet. When I measured by buffer circles around my hospitals, they seemed small. So, after measuring, I realized that I needed to change my 3^rd argument to be 1000 Meters to define my unit of measurement.

        https://pro.arcgis.com/en/pro-app/latest/tool-reference/analysis/how-buffer-analysis-works.htm

3        Dissolve- The last tool in my script required me to dissolve the buffer rings I just made, so I ran the arcpy.management.Dissolve() and passed in my previous created file, then set the new file name to be hosXY_buffer_Dissolve, but then things got challenging. I set the next two arguments to NONE as they are optional to fill in. I then set the 5^th argument of my tool to Multi Part, and the last one was Dissolve Lines. This allowed my dissolve tool to get rid of the overlapping lines that my buffer file was displaying around the hospitals.

        https://pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/h-how-dissolve-data-management-works.htm

4        Printing out the terminal output – I ran a print statement after each tool that I ran using the arcpy.GetMessages() which returns an index of messages for running a tool .This includes the start time, errors, if it succeeded, when it succeeded, and the time that it took to run this tool. I also concatenated a + “\n” to create a space between each script’s output in my terminal.

        https://pro.arcgis.com/en/pro-app/latest/arcpy/functions/getmessages.htm

5        Importing modules / Overwriting the Output / Workspace- I imported ArcPy, set my workspace to arcpy.env.workspace = “my file path to my project in module 3”, and then I set my arcpy.env.overwriteOutput to True so I would not have to delete the files that I kept creating in my script as I was running and testing my Python file.

        https://pro.arcgis.com/en/pro-app/latest/arcpy/get-started/importing-arcpy.htm

6        Checking arc Pro for results – During my script and at the end of my script, I made sure to check the files in Arc Pro to ensure my script ran correctly. The files were locked so I had to save arc Pro and close the software when running the IDE. However, since I did the step above with the overwrite Output = True. I did not have to delete the files I created every time I ran the script. I made sure the hospitals XY shapefile was correctly on the map with X and Y coordinates in the attribute table, then I check ed for the buffer ranges around the hospitals. I then looked in the project’s GDB to ensure the buffers_dissolve feature class was there, and that the buffer ranges showed the dissolved buffer rings around the hospitals in the dissolve feature class. I also measured the buffer rings to make sure they were 1,00 meters (the first few times I ran the tool the ranges ended up being in feet and not meters).

                    Double Checking Your Work Is Crucial!

Final Output:

So we talked about building a model, and building a custom Python Script. Both are great for automating geoprocessing workflows in GIS and demonstrate multiple ways of automating workflows to solve complex problems. 

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