Intersection Tutorial

Overlay analysis is a common and useful GIS processing task. Esri defines overlay as follows:

"Overlay processing combines two or more layers into one single layer. You can think of overlay as peering through a stack of maps and creating a single map containing all the information found in the stack, for example:

What parcels are within the 100-year floodplain? (Within is just another way of saying on top of).

What roads are within what counties?

What land use is on top of what soil type?"

Or, to answer our question:

Which zip codes does each water district serve?

We will use the Intersect tool in ArcGIS to perform the overlay analysis. This tool's help states: "Features or portions of features which overlap in all layers and/or feature classes will be written to the output feature class." This means that if we intersect our zip codes data with the water districts, only the portions of zip codes which overlap the water district will be kept, which is just what we need.

This tutorial continues from the end of the Digitizing tutorial. You should now have the polygon(s) for the Spartanburg water district boundaries.

Getting Started:

1. Open your previous map document OR start a new, blank ArcMap document.

2. In ArcMap, maximize the ArcCatalog pane on the right side of the screen (if necessary).

3. Connect to the local LadnerCI folder (if necessary).

4. If necessary, add the WaterDistricts.shp shapefile OR the WaterDistricts feature class from the Spartanburg geodatabase, whichever has your completed polygon(s).

5. Add the SC_zip_stateplane shapefile OR feature class to the map by dragging it over from the ArcCatalog pane.

Using the Intersection Tool:

Let's find the Intersection tool and use it. Note that this tool is going to output a feature class to a geodatabase.

1. In ArcMap, Press Ctrl + F on the keyboard to open the Search pane.

2. In the search bar at the top of the pane, type intersect and hit enter or click the magnifying glass icon to search.

3. Click the name for the Intersect (Analysis) (Tool), which comes up first in my list. The tool dialog opens.

4. Use the Input Features drop down menu to add WaterDistricts and SC_zip_stateplane to the list.