Module 7 - Explore/Manipulate Spatial Data

This week's lab was one of the tougher ones... probably because the majority of the code was written without much code-building help from ArcGIS tool syntax. The goal for this lab was to create a new geodatabase, populate said geodatabase with pre-existing shapefile data, then create and populate a dictionary of County Seat cities in New Mexico (using the data that was copied into the new geodatabase).

Screenshot (in two parts) of the Module 7 script results.

Rough pseudocode generally replicating the above is as follows:
Start
     Set workspace environment
     Create new geodatabase
     Print shapefile feature class list
     Copy shapefile data to the new geodatabase
     Set SearchCursor to identify each city that is a county seat
     Create a new dictionary
     Populate the new dictionary with all cities that are county seats
          Key = City Name, Value = City Population
     Print the county seat dictionary
End

Just after the point when I copied the shapefile data to the new geodatabase is where things started to get a bit hairy... While there were problems with my original code attempts using the SearchCursor method, the real issues lay with the fact that my geodatabase didn't initially populate! This was a little something I figured out after several attempts to run the code - once I was locked out of my dataset (and decided to delete the geodatabase in ArcCatalog to start over) I found that I couldn't expect my code to search a cities feature class if it never actually existed in my geodatabase in the first place! The solution was to use the arcpy.ClearEnvironment function... after that I finally had a working code.

My success was short-lived - getting the dictionary to populate was also not so easy for me. The hint in the lab was that the code need to iterate within a for loop, and an example of how to set up the iteration was even provided. It sounded simple (and looking back on it, it IS simple) but this single step took me hours to get through. To summarize my problems and solution mini-drama:

• The original SQL query used from my previous SearchCursor step had been deleted after that step... so I needed to re-write that bit of code.
• The for loop needed its iteration cycle set up... first by defining my variables, then by plugging these variables into the iteration code suggestion.
• The number used to define the for loop variables needed to match the placement of my variable within my SearchCursor code; for example, if my city was listed first within my SearchCursor then it needed to be listed as [0] within my for loop code.

Such small details caused a world of grief... and learning! Hopefully I won't be forgetting these lessons anytime soon.