Ask A Cartographer

Labels of proportional symbols

September 05 2011 | 1 comment
Categories: ArcGIS 10, Map Elements, Page Layout

Is there a way to format labels when using proportional symbols? I'm using ArcGIS 10 and there doesn't seem to be a way to do that; slowly double-clicking the label in the table of contents does not produce any result. (I'm using ratio data for the value; the data does not need to be normalized).

In addition, I can choose to have up to 12 symbols displayed in the legend. Why are only 5 symbols ever shown, at most--even if I choose to display more than 5?

Thank you for the information.

Mapping Center Answer:

There isn't a way of formatting labels in the Table of Contents but, of course, you can alter their appearance when you add a legend to a Layout.

The second problem is most likely a bug and this has now been passed to the developers to look into.  However, if you are creating a proportional symbol map our advice is that you shouldn't need more than a few 'visual anchors' in your legend.  The attachment shows how you might design a legend for proportional symbols.  These can be created by adding a legend to your Layout, Converting to Graphics and then rearranging the individual graphic components as you wish.  You can add lines and other components using the Draw tools.

There may also be some ideas in this Mapping Center blog post on Bar Chart Legends that you can use when thinking about Proportional Symbol legends. many of the ideas are transferable.

update posted by Kenneth Field on Sep 9 2011 4:12PM
The development team have reported that it is not a bug but that the renderer is trying to present a reasonable sampling of values to show and that sampling is based on three inputs: the min field value, the max field value, and the number of classes requested. The renderer takes these as input and tries to produce an escalation of values that break at nice values. A value that is near to the maximum value is rounded to a logical nearest power of 10 value.

That said, the issue has been noted and will feed into development work to make it clearer to users what is going on. Hope this helps explain and thanks for alerting us!

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