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7. Understanding Polygons
Custom geographic shapes (or polygons) are relatively easy to create in Tableau. In this lesson, We'll go through how to how take geographic coordinates from 4 different locations and convert into a polygon in Tableau.
- Custom shapes that can be superimposed on maps or building plans
- Rely on longitude / latitude coordinates for each point
- Require an ordering column so that points are connected to each other correctly
- Place the ordering column on PATH to ensure the shape is created correctly
As we've seen with filled maps of the United States in previous lessons, Tableau has some in-build mapping libraries that can quickly find countries, states, or provinces. However, sometimes when you're creating maps, you'll want to create some custom areas such as sales territories or more granular administrative regions such as post codes or boroughs. To do this, we need to use polygons and an example of a polygon map is shown onscreen. For each individual selected region is a borough of London. So how do we create these types of shapes? Well, at their base level, polygons are a set of longitude and latitude coordinates given a specific order that represents an individual area on a map.
Used correctly, polygons can add a lot of insight to geographical data and make your insights much more intuitive to the viewer. Let's start by viewing the raw data of a sample polygon in Excel. Similar to our root data, each row in the dataset represents an individual point with longitude and latitude coordinates. We also give each point a polygon ID, which tells Tableau the order in which to connect each point. And then finally, we want to give our polygon a name, so if we have multiple polygons, the points won't get mixed up when we add all of these points onto the map. Let's now plot this simple polygon in Tableau.