Vector Overlays

Before tackling this tutorial, you will need to download and install a dataset following these instructions:

Create a folder called overlays somewhere under your personal directory (e.g. C:\Users\jdoe\Documents\Tutorials\overlays\).
Download the data for this exercise then extract the contents of overlays.zip into your newly created overlays folder.

Buffering a layer

In this exercise, you will buffer the Augusta point layer using a buffer radius of 30 miles. This will create a polygon from a point layer. Note that the buffer operation can be applied to point, polyline and discrete polygon vector layers. Also, note that buffering is not technically a vector overlay operation, but it can often be used in conjunction with vector overlay operations.

You might want to buffer a feature if you are, for example, interested in identifying features from another layer that fall within a certain distance from the said feature.

Open the Overlays.aprx file.
Bring up the geoprocessing window. Recall that the geoprocessing tool can be accessed via the Tools button under the Analysis tab.
The Buffer tool may already be present under the Favorites tab, if not, type Buffer in the search field.
Open Buffer (from the Analysis Tools).

Select Augusta from the Input Features list.
Name the output Augusta_buffer.shp (save it in the overlays/ folder and not the Default geodatabase).
Set the distance to 30 (US survey) miles.
Set the method to Planar.
Click on Run.

You'll note that the output is a polygon layer even though the input is a point layer. The buffer, therefore, encompasses an area.

The buffered layer also adds an attribute to its table: the buffer distance attribute BUFF_DIST. However, the value will be reported in the mapping units and not necessarily the distance unit specified in the buffer tool. In this example, the mapping units are meters, hence the reason you see the value of 48280 in the BUFF_DIST attribute (30 miles = 48280 meters).

Clipping a layer

Next, you will learn how to clip features using a polygon "clipping" layer. In this example we will use the recently created buffer layer to clip out all counties (or section of counties) from the Maine layer that fall inside the Augusta_buffer layer.

Navigate back to the Geoprocessing window's main landing page (by clicking on the Back arrow).
Type "Clip" in the Search bar.
The Clip tool from the Analysis Tools toolset should be the first tool returned

Open the Clip tool.
Select the Maine layer as the layer to be clipped.
Select the Augusta_Buffer layer as the Clip Features.
Name the output Counties_clip.shp.
Click Run.

The output shows the areas that fall within 30 miles of the Augusta point layer. You may need to change its symbology to differentiate it from the background Maine layer.

Note that this output differs from the output of a Select Layer by Location geoprocess in that the latter would return (select) the entire polygon features even if just parts of that feature fell within the 30 mile buffer polygon.

The clip tool "cookie cuts" out the polygons thus limiting the output to just the areas of the clipped layer that fall inside the polygon.

The clipped output carries over the attributes from the input layer (i.e. the layer that was clipped). The one difference is that the number of features may be less in the clipped layer if the clipping feature did not encompass all the features from the input layer.

In our example, the Counties_clip layer has the same attributes from the Maine layer, but it has fewer records. Note that it does not carry over attributes from the clipping feature (i.e. Augusta_buffer).

Intersecting two layers

In this exercise you will perform another type of overlay where you will intersect the Maine layer with the Augusta_buffer layer.

In the Geoprocess window, bring up the Intersect tool (you might already see this tool under the favorites tab)

Next to the Input Features field name, click on the down arrow to bring up the layers present in your Contents pane.

This step will auto-populate the field with a list of layers present in your Contents window.

From the aforementioned pull-down menu, select the layers that are to be intersected: Maine and Augusta_Buffer.
Click on the Add button in the lower-right side of the pull-down menu.

Note that you can intersect more than two layers.

Name the output maine_augusta_intersect.shp. Be sure to save it in the ./Overlays folder (and not in a geodatabase).
Click Run.

At first glance, the output looks no different from the clipped layer. But if you look at the attributes table, you'll note that the output layer has attributes from both input layers. Intersect will output both attributes and features from both layers that share the same spatial extent.

If a conflict in attribute name occurs, the software will append a number to the end on the attribute name. For example, both input layers have a column called "NAME". This results in an output column, NAME, from the input Augusta_buffer layer, and an output column, NAME_1, from the Maine input layer.

Note that a polygon can also clip and intersect points and polyline features (and not just polygons). Try it out for yourself!

Unioning two layers

In this last step, you will union two layers. This will result with all features in the two layers being present in the output.

In the Geoprocessing pane, search, then open, the Union tool.
In the Union tool, click on the Input Features pull-down menu and select

Name the output union.shp.
Click Run to complete the union operation.

The output includes all features and attributes from both layers. Where boundaries don't overlap, the tool splits one layer's polygons with the layer's polygon outline.

For example, Franklin county consists of a single polygon in the Maine layer. Because the Augusta_buffer polygon boundary crosses Franklin county, its boundary splits Franklin county into two parts.

Save your project. This wraps up this tutorial.

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