With symbol maps, marks on the map are not drawn as filled regions; rather, marks are shapes or symbols placed at specific geographic locations. The size, color, and shape may also be used to encode additional dimensions and measures.

Continue your analysis of Superstore sales by following these steps:

1. Navigate to the Sales by Postal Code sheet.
2. Double-click Postal Code under Dimensions. Tableau automatically adds Postal Code to the Detail of the Marks card and Longitude (generated) and Latitude (generated) to Columns and Rows. The mark type is set to a circle by default, and a single circle is drawn for each postal code at the correct latitude and longitude.
3. Drag Sales from Measures to the Size shelf on the Marks card. This causes each circle to be sized according to the sum of sales for that postal code.
4. Drag Profit from Measures to the Color shelf on the Marks card. This encodes the mark color to correspond to the sum of profit. You can now see the geographic location of profit and sales at the same time. This is useful because you will see some locations with high sales and low profit, which may require some action.

The final view should look like this, after making some fine-tuned adjustments to the size and color:

Sometimes, you'll want to adjust the marks on symbol map to make them more visible. Some options include the following:

• If the marks are overlapping, click the Color shelf and set the transparency to somewhere between 50% and 75%. Additionally, add a dark border. This makes the marks stand out, and you can often better discern any overlapping marks.
• If marks are too small, click on the Size shelf and adjust the slider. You may also double-click the size legend and edit the details of how Tableau assigns size.
• If the marks are too faint, double-click the color legend and edit the details of how Tableau assigns color. This is especially useful when you are using a continuous field that defines a color gradient.

A combination of tweaking the size and using Stepped Color and Use Full Color Range, as shown here, produced the final result for this example:

Unlike filled maps, symbol maps allow you to use size to visually encode aspects of the data. Symbol maps also allow for greater precision. In fact, if you have latitude and longitude in your data, you can very precisely plot marks at a street address-level of detail. This type of visualization also allows you to map locations that do not have clearly defined boundaries.

Sometimes, when you manually select Map in the Marks card drop-down menu, you will get an error message indicating that filled maps are not supported at the level of detail in the view. In those cases, Tableau is rendering a geographic location that does not have built-in shapes. Other than cases where filled maps are not possible, you will need to decide which type best meets your needs. We'll also consider the possibility of combining filled maps and symbol maps in a single view in later chapters.