Polygon in Polygon Overlay

Introduction

In this exercise, you will learn how to perform a union between overlapping polygon features using the AreaOnAreaOverlayer. The AreaOnAreaOverlayer is typically used for three main operations: 

1. Deconstruct overlapping polygons to produce the intersections and differences

2. Compare multiple datasets for area overlaps

3. Area calculations based on overlapping area data

Data Source

The first source is historic zones in the City of Vancouver, which is in the Neighborhood GeoPackage dataset. 

The second source is the neighborhood boundaries in the City of Vancouver, which are also in the Neighborhood GeoPackage dataset. 

Step-by-step Instructions

In this scenario, you will be performing area calculations based on overlapping historic zones and neighborhood polygons. This will allow you to identify which historic areas belong to each neighborhood and the total area of each historic zone.

The data used in this tutorial can be found in the Files section of this article.

1. Create a New Workspace

Open FME Workbench and create a blank workspace. 

2. Add an OGC GeoPackage Reader

Add a reader to the canvas by clicking on the Reader button on the top menu bar or by going to Readers > Add Reader. In the Add Reader dialog, set the following:

• Format: OGC GeoPackage
• Dataset: Neighborhoods.gpkg
  • Click on the ellipses to navigate to the location of the file on your computer

Click OK and the Select Feature Types window will open

This GeoPackage contains two tables. After clicking OK, the Select Feature Types dialog will appear. Select both Neighborhoods and HistoricZones, then click OK twice to add the reader to your canvas. 

3. Overlay Polygons

To filter the data spatially, we will use an AreaOnAreaOverlayer transformer. Select both the HistoricZones and Neighborhoods reader feature types, then add an AreaOnAreaOverlayer to the canvas by typing “AreaOnAreaOverlayer” to bring up the list of FME Transformers in the Quick Add Search. Select the AreaOnAreaOverlayer from the list of Transformers by double-clicking or by using the arrow keys and the Enter key to add it. 

Double-click on the AreaOnAreaOverlayer to open the parameters. In the parameters, set the following:

• Accumulation Mode: Merge Incoming Attributes

Click OK. 

4. Calculate Polygon Area

Since we are creating new polygons, let’s calculate the new area. Add an AreaCalculator to the canvas and connect it to the Area output port on the AreaOnAreaOverlayer. We can accept the default parameters. 

5. Run Workspace

Connect an Inspector transformer to the AreaCalculator Output port. 

Run the workspace by clicking the Run button on the top toolbar, or by selecting Run > Run Workspace from the top menu bar. 

After running the workspace, new polygons will be created for each HistoricZone in each Neighborhood, with a newly calculated _area. 

Data Attribution

The data used here originates from open data made available by the City of Vancouver, British Columbia. It contains information licensed under the Open Government License - Vancouver.