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- In the Table of Contents, Ctrl-select the PrecipStations_StatePlane and Watersheds_StatePlane layers.
- Right-click either selected layer and select Zoom To Layers.
- Open Geoprocessing pane by clicking Tools from Analysis tab.
- Double-click the Analysis toolbox then the Proximity toolset then the Create Thiessen Polygons tool.
Before populating the variables in this tool, you will change an Environment setting so that the polygons are calculated for the entire region that you just zoomed to. - At the top of the Geoprocessing window, click the Environments button on the right.
- For Extent, use the drop-down menu to select Current Display Extent and go back to Parameters.
- For ‘Input Features’, drag in the PrecipStations_StatePlane layer.
- For ‘Output Feature Class’, rename the feature class from “PrecipStations_StatePlane_Cr” to “PrecipThiessen”.
- Use the ‘Output Fields’ drop-down menu to select All fields.
- Ensure your ‘Create Thiessen Polygons’ window appears as shown below and click Run.
You will notice that polygons now fill the entire Map Display indicating which areas are closest to which rain gages. - Open the PrecipThiessen layer attribute table.
Notice that all of the fields that you originally downloaded from CDO are still included, because you selected to output all fields when running the Create Thiessen Polygons tool. If you do not see all of the same fields, re-run the tool and this time output all fields. - Close the Table.
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