Module 5 - Exploring & Manipulating Data

This module provides an in-depth examination of methods for exploring spatial data, including checking for datasets, describing, and listing data in a workspace. Additionally, it addresses the utilization of lists, tuples, and dictionaries, as well as the application of for loops in lists. For loops are fundamental tools in Python for working with lists and other iterable objects. They allow you to execute a block of code repeatedly, once for each item in the list.

In the second segment of the module, which focuses on data manipulation, we are introduced to the use of cursors for data access, the integration of SQL within Python, and the management of table and field names. The module places a strong emphasis on the use of cursors to traverse table rows, highlighting various types for executing search operations, adding new records, and updating existing ones. Furthermore, it covers the essential topic of validating text and field names to ensure data integrity.

In this lab, we will develop a script composed of three code blocks. The initial block is designed to establish a new file geodatabase (fGDB) and transfer existing shapefiles from the Data folder into the newly created geodatabase. The second block involves creating a Search Cursor to extract and display the city NAME, FEATURE, and POP_2000 fields for cities identified as 'County Seats'. Lastly, we will initialize an empty dictionary and fill it with the names (as keys) and populations (as values) of all County Seat cities and utilizing a for loop to print the dictionary.

After importing the necessary modules and classes, and setting overwriteOutput to True, we created an empty geodatabase in the Module5/Results folder using the arcpy.CreateFileGDB_management statement. Next, we defined the fclist variable to enumerate all feature classes in the current workspace, followed by creating a for loop to transfer all features from the Data folder to the new geodatabase (fGDB).

When transferring shapefiles to a file geodatabase (fGDB), it is essential to modify the names appropriately. The default naming convention for shapefiles includes the file extension “.shp,” which must be removed. it necessary to use the Describe() functions basename property of shapefiles when copied via Python script from a folder to a file geodatabase. The script utilizes the basename property of the feature class instead of the default name for the feature class that is stored within the fGDB.

The subsequent section of the script involves establishing a Search Cursor for the cities layer to retrieve the Name, Population (POP_2000), and Feature of all cities designated as 'County Seat' in the Feature field. To achieve this objective, we must first configure the workspace to the new fGDB workspace. Once the variables are set and the Delimited field is established, we created a Search Cursor. We then utilize a for loop within the cursor to display all the cities' NAME, POP_2000, and FEATURE categorized as 'County Seat.'

The last block of code in the script is to create an empty dictionary and populate it with names (keys) and populations (values) of each 'County Seat' city, and print the populated dictionary using a for loop. This final step of the lab assignment presented significant challenges for me. I successfully created the empty dictionary and implemented the for loop utilizing the format <dictionary variable>.update({<key>:<value>}). However, upon execution, I did not encounter any error messages, yet the output was not as anticipated. I reviewed the materials from Module 5, including exercises and lectures, and conducted further research online, but I was unable to identify the error. I discovered that the print statement had incorrect indentation; after correcting the indentation and rerunning the script, the script ran successfully and the output met my expectations.

Here is a screen shot showing the output of the Module 5 Python script       

              

Module 5 Python script flowchart