Displaying symbols on a map

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1. Overview

A symbol is a type of map element that is used to represent location points on a map.

Using size rules, the size of a symbol can be varied according to corresponding data values. For example, in a proportional symbol map, each symbol indicates the location of a city, and the size of the symbol represents a range of corresponding sales figures (or other measure values).

Additionally, using color rules, the color of each symbol can be varied according to data values.

The following walkthrough shows you how to create a proportional symbol map in which the location of the symbols comes from the data and both the size and color of each symbol varies according to data values.

This article describes features available in Dundas BI 2.6 or later.

2. Prepare location and measure data

Consider the following Excel spreadsheet which specifies the decimal longitude and latitude for various cities in Canada. These values will be used to create and position symbols on the map. In addition, the spreadsheet contains some measure data such as population and sales figures for each city.

Excel spreadsheet with location and measure data
Excel spreadsheet with location and measure data

Create a data connector in Dundas BI by dragging this spreadsheet from Windows Explorer to Dundas BI Explore.

3. Add a map visualization

Create a new dashboard based on the Blank template. Go to the toolbar, click Data Visualization, and then click Map. An empty map visualization is added to the canvas.

Select the map visualization and click Properties. Scroll down and look for the Show Only Requested Maps checkbox. Enable this option to turn off the automatic map loading behavior and make it so that only map resources you specifically drag from Explore are displayed.

Show Only Requested Maps property
Show Only Requested Maps property

Go to Layout properties and set the Map Projection to Mercator. This is one of the more commonly used map projections. The Mercator Projection covers the earth from −180° to 180° longitude, and 84° north and south.

Use the Mercator map projection
Use the Mercator map projection

4. Add a map resource

Go to Explore and expand the Maps \ Shared \ States and Provinces folder.

Drag the Canada (States and Provinces) map from Explore and drop it onto the empty map visualization. This is one of the built-in map resources included with Dundas BI.

Drag a map resource
Drag a map resource

You won't be able to see the map though because data has not been added yet.

5. Add data to the map

Locate and expand the Excel data connector in Explore. Drag the CityName column and drop it onto the map visualization. You should now be able to see the map of Canada, except that the shapes appear in the top left corner. The reason for this is that the viewport of the map is configured by default to display the world map. You will need to switch to View mode to pan and zoom in as needed (e.g. by using mouse wheel). Switch back to Edit mode when done.

Pan and zoom the map in View mode
Pan and zoom the map in View mode

Next, drag the Population and Sales columns from Explore and drop each one onto the map. These will be added as measures as shown in the Data Binding Panel. Edit the Population measure and change its Format to N0.

Drag CityName column to map
Drag CityName column to map

Note that the map does not display any symbols yet because they will be generated dynamically from location data.

5.1. Symbol Compatible Name

The following is a side-topic which is not part of the walkthrough.

If you click Bindings in the Data Binding Panel, you'll see that the SYMBOL NAME binding is bound to the CityName column from the Excel data. This is the binding that is necessary for matching symbols with your data.

Symbol name is bound to the CityName column
Symbol name is bound to the CityName column

If you're using pre-defined symbols from a map resource (instead of generating them from location data), you need to make sure the names of the pre-defined symbols can be matched with the bound data values. Otherwise, you must change the bound data (e.g. CityName values), or give each symbol element a Symbol Compatible Name to facilitate data binding.

For example, your CityName data has a New York City entry but in your map resource, the symbol is named New York instead. Matching will fail in this case but what you can do is edit the properties of this map symbol in Dundas BI and set its Symbol Compatible Name property to New York City. This needs to be done for each symbol element that fails to match.

Symbol Compatible Name property for a map symbol
Symbol Compatible Name property for a map symbol

6. Bind symbol locations

Open the Data Binding Panel for the map and click Bindings in order to modify the visualization bindings.

Scroll down to find the SYMBOL LONGITUDE and SYMBOL LATITUDE bindings.

Go to your Excel data connector in Explore and drag the Longitude column onto the SYMBOL LONGITUDE binding. Similarly, drag the Latitude column onto the SYMBOL LATITUDE binding.

Symbols for each city are now displayed on the map.

Add Longitude and Latitude bindings
Add Longitude and Latitude bindings

If you switch to View mode you can access a tooltip on each city that shows its name, population, and sales figure.

Symbol tooltip
Symbol tooltip

You can configure symbol tooltips from the Bindings tab or from the map's Text properties.

7. Symbol color rules

The symbols on the map have different colors because of a symbol color rule which was added automatically and which corresponds to the first measure, Population.

Symbol color rule
Symbol color rule

Click Auto Color Rule to make adjustments to the From Color or To Color. You can also change the Number of Classes (i.e. number of data ranges) that are generated and the Distribution method which determines how data points (i.e. symbols) are slotted into the various classes.

Symbol color rule properties
Symbol color rule properties

7.1. Distribution methods

The default distribution method is Equal Distribution which divides the entire data range into intervals containing the same number of data points, resulting in a more uniform-looking map.

The Equal Interval distribution method divides the entire data range into equally spaced intervals. This method may not be the best option when your data is distributed unevenly because the data points might be slotted into a single or very small number of intervals.

The Continuous distribution method maps the entire data range to the color range in a continuous fashion.

8. Bind to symbol size

Open the Data Binding Panel for the map and click Bindings in order to modify the visualization bindings.

Scroll down to find the SYMBOL SIZE binding. Click to add the Sales measure to this binding.

Bind symbol size to Sales measure
Bind symbol size to Sales measure

The sizes of the symbols now vary according to sales figures for each city. Similar to color rules, a symbol size rule has been automatically generated. You can modify this rule in the same way as color rules, except that instead of a range of colors, you set a range of sizes.

Symbol size rule properties
Symbol size rule properties

9. Add a legend

Both symbol color rules and symbol size rules have a Display In Legend property which is enabled by default. Simply add a legend to the canvas from the Data Visualization toolbar and bind it to the existing map. The legend will automatically display items corresponding to the different color and size data ranges.

Legend items generated from symbol color and size rules
Legend items generated from symbol color and size rules

10. Notes

10.1. Loading map content automatically

By default, the Show Only Requested Maps property is turned off for a map visualization, which means the map will load content from built-in map resources automatically when there is a match with the metric set data added to the map.

For example, add a blank map visualization to the canvas and then drag the CityData Excel spreadsheet (Sheet1) onto the map. The map visualization will automatically load a built-in map resource containing symbols with names matching the CityName column. The viewport of the map will also be adjusted automatically to center upon the matching symbols. Symbols that do not match the data may still be loaded but these will appear with a grey, semi-transparent color. The use of semi-transparency allows overlapping symbols to be detected. Data-bound symbols will be displayed with color due to the symbol color rule which is also added.

Symbols are automatically loaded after adding Excel data to the map
Symbols are automatically loaded after adding Excel data to the map

11. See also

 

Dundas Data Visualization, Inc.
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Toronto, ON, Canada
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International: 1.416.467.5100

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