how to create a ring map
I recently saw an interesting article in the Winter 2008
ArcUser magazine that demonstrated the use of ring maps
to present a fictional set of time series data for the
weekly disease alert status in Washington, DC.
I am an ArcView 9.2 user and would like to know how to
create those kind of ring maps. Thanks for your help.
Mapping Center Answer:
There isn't anything in ArcGIS that will produce these graphics automatically; the closest thing is the data clock in the Tracking Analyst.
That said, you could certainly do the work manually as follows:
1. Create a new feature class, start editing and add a circle around the features you want to build the graph around.
2. Buffer the circle with the number of rings that you want (number of time intervals). This would create buffer features. Add a field to the buffers and set each ring's value to be the label for the time interval the ring represents.
3. Select all the buffers and use the Cut Polygon edit task to cut across the circle, intersecting its center. (Tip: draw a graphic marker at the center--delete it when finished with step 4)
4. Repeat step 3 until the proper number of wedges around the circle have been created.
5. Add a field to the cut up buffers and set its values according to your time values.
I would symbolize all polygons with an outline--so that the intervening (empty) polygons would be shown with lines to help give visual continuity.
If your shape is not easily fit into the circle (e.g., like the second example in the the enclosed article), construct a nicely curved polygon (instead of a circle) and buffer that. If you do this, you have the opportunity to exaggerate the size of the curve to handle imbalances in your geography's feature density.
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