Creating Features in ArcGIS

Workshop #3: Creating Features in ArcGIS (part 2) and

In the last workshop we learned how to create different types of spatial data – points, centroids, and buffers. Today, we will learn how to do one more type of trade area analysis – Thiessen Polygons. Contrasted against buffers, each presents a different way of determining the extents of a stores traded area, which can have different implications for analysis. Once these methods have been used, you could use them to create a map similar to the one you made last week. However, due to time constraints you will just have to submit a screenshot of your work at the end of the workshop to get the completion grade.

A. Getting Started

• Log into the remote desktop using your username and password.
• In lab instructions I use >for click, >dc for double click and >rc for right click
• Throughout this workshop, you will see references to ‘your workspace’ à this means the folder that you saved all your data to when you downloaded it from D2L.

• Please note: the data that we are using here is the same as last week. We will be working out of the MXD document you saved when you completed Workshop 2. In it, there should be a census tract file, the point locations of the Lowe’s stores, and the buffers you created. Please see last weeks instructions if there are any layers listed in the Table of Contents with a red exclamation point (!).

B. Creating Thiessen Polygons

• In the ArcToolbox à Analysis Tools > Proximity > Create Thiessen Polygons
  • Input Features: select Lowes from the dropdown list
  • Output Features: press the file folder to the right, and save as Lowes_Thiessen to your workspace.
  • Press the Environments… button and a list of options will appear. Click processing extents, and in the dropdown box Extent, select the option “Same as layer GTA census tracts” and press OK à setting the environment makes sure that Thiessen polygons are created that cover the entire GTA study area. If this was not selected a smaller area might be used. This is important to keep in mind for all geoprocessing.
  • You will see a new layer appear on the map as a polygon, and the corresponding layer appear in the Table of Contents (Lowes_Thiessen). If you open the attribute table, you will see that all the information from the point file has automatically been transferred into the polygon shapefile.

C. Spatial Joins

The last tool you will learn about is spatial joins. This tool allows information to be consolidated or transferred between layers – even if they are of different types – based on spatial proximity. This final section will show you how to use this two ways.

C1. Spatial Join

• Open the attribute table for Lowes_Traded_Area. You should find an essentially empty table. We will join the store information stored in the Lowes point layer.
  • In the ArcToolbox à Analysis Tools > Overlay > Spatial Join (again, remember that a help file is automatically loaded on the right side of the dialogue box that opens).
    • Target Features: Lowes_Traded_Area
    • Join Features: Lowes
    • Output Feature Class: press the file folder to the right, and save as Lowes_TA_J to your workspace
    • Join Operation: JOIN_ONE_TO_ONE
    • For this process, keep the box checked for ‘Keep All Target Features (optional)’
      • Below is the list of all the fields in the attribute table for Lowes layer that will be joined to Lowes_TA_J
      • For now, we will keep them all.
    • Press ok
• Open the attribute table for Lowes_TA_J. You should find a complete table with all the store information.

C2. Calculating the Sum of Values of Points Within a Polygon using Spatial Join

• In the ArcToolbox à Analysis Tools > Overlay > Spatial Join
  • Target Features: Lowes_TA_J
  • Join Features: GTA_Census_Tracts
  • Output Feature Class: keep the defualt
  • Join Operation: JOIN_ONE_TO_ONE
  • For this process, keep the box checked for ‘Keep All Target Features (optional)’
    • Below is the list of all the fields in the attribute table for Lowes layer that will be joined to.
    • At this step, you only want population, scroll down until you find CTUID (Text) > select and use the X to the right of the list to delete it. Delete all fields listed below it except Population (Long).
    • rc Population (Long) > Merge Rule > Sum à this will determine what value is stored in the attribute table. Here it will be the total population within the census tracts that overlap with the traded area you drew around each Lowes store.
  • Press ok
• Open the attribute table for Lowes_TA_P. You should find a complete table with all the store information.

C3. Saving the Data

Now that we have created this new spatial data file, we need to save it!

• In the Table of Contents > rc on Lowes.txt Events > Data > Export Data…
• Select the file folder to the right of the textbox > save the new file in your workspace as Lowes_TA_P shp (make sure the Save as Type is Shapefile)

This process can be done with the buffer layers as well.

For this Workshop, export the attribute table as a text file and upload it to D2L to receive the completion grade.