Great Plains Farming

Winter wheat was the primary crop on the Great Plains in the 1930s. The promise of riches from the sale of this crop in the east had brought farmers to the plains in ever increasing numbers during the last decades of the 19th and the first decades of the 20th centuries. Along with increasing demand for the crop, particularly during and after World War I, and the introduction of mechanized farming, vast stretches of the plains were plowed under to wheat and other crops.

An Example to Get You Started -

How much of the available land in the Dust Bowl region was farmed? Census data from 1930 can help give us a picture of just how intensively the land was used.

Load your GIS software and open the Dust Bowl project file. Display these layers:

  • Great Plains States 1930
  • United States
  • North America Relief Map

making sure that all other layers are off at this point.

In order to determine what percentage of the available land was farmed we need to look first at the list of available census data categories in the Great Plains Farming worksheet. Notice that the percentage you want to examine is not a part of the list. You will need to do some simple arithmetic to normalize the data, dividing the number of acres harvested by the total number of acres available:

HARVESTAC / LANDACRES

My World
ArcGIS
• Click on the Analyze tab, select to Add Field(s) By Math Operation, and complete the form as follows:

• Double click on the Dust Bowl Counties Census Data - 1930 layer to bring up the Edit Appearance window pictured below:

• You can choose the Colorscheme you want to use. Enter 5 as the Number of Fill Colors and select to Classify By: Quantiles. This will give you five groups with approximately the same number of counties per group. Click on the Apply button and Close the window. Set the level of Transparency to 50% if you would like to see the terrain through the new map layer.

 • Right click the Dust Bowl Counties - 1930 layer in the table of contents and select Properties....

• Click on the Symbology tab and select Quantities.

• In the Fields pane select Harvested Cropland as the Value and Land Area as the Normalization value.

The result is the is the desired division. It is said to be a normalized value because we now have a rate that is not affected by the size of the county.

• In the Classification pane click the Classify button. You will see a new window. Select to classify by Quantiles and 5 classes as pictured below:

This will give you five groups with approximately the same number of counties per group.

• Click OK

• You can define your own labels to make the map easier to read by editing the values in the Labels column:

• Click the Display tab and set Transparent to 50% if you would like to see the terrain through the new map layer.

• Click OK again to leave the Properties window.


Once the data is available it is easy to prepare a map of the results like the one below.

My World
ArcGIS
• Select File >> Layout & Print from the main menu.

• Uncheck the Show Scale and Show Compass boxes in this case.

• Click Print

• My World prints an image of the map to a file. Name the file and Save it where you can get to it from your word processor.

 • Select View >> Layout View from the main menu.

• A map template is provided for you to edit. Double click on:

- Map Title to enter your own title
- Created by to add your name and today's date

• Zoom in () and/or pan () to position the map image as desired.

• Select File >> Print from the main menu. Check to see that the correct printer is selected and that the orientation of the map is correct.

• Click OK to print your map.

• Select View >> Data View from the main menu.


Your turn. Prepare a similar map for 1940. You will go through the same steps except that this time you need to define the same classification scheme as in the previous map. This will allow you to examine the results on a comparable county-by-county basis.

My World
ArcGIS
• Click on the Analyze tab and set up the division to create the new percentage as you did for the 1930 data.

• Double click on the Dust Bowl Counties Census Data - 1940 layer to bring up the Edit Appearance window and copy the settings from the Dust Bowl Counties Census Data - 1930 layer. Double click on values in the To column to copy values from the other layer. Values in the From column will be automatically adjusted:

• Click OK

 • Right click the Great Plains States 1940 layer in the table of contents and select Properties....

• Click on the Symbology tab and select Quantities.

• Click on the Import button and select to Import symbology from the Census 1930 layer:

• Click OK

• Click OK once again and the classification of the data is defined as before.

Print a copy of your new map and compare your two maps side-by-side.

To Start You Thinking -

1) Where was farming practiced the most intensely in the Great Plains in 1930? in 1940?

2) How does the intensity of farming compare in different parts of the Great Plains from 1930 to 1940?

data from " Gutmann, Myron P. GREAT PLAINS POPULATION AND ENVIRONMENT DATA: On-Line Extraction System [Computer file]. Ann Arbor, MI: University of Michigan [producers], 2005.

Last modified in July, 2008 by Rick Thomas