I’ll add some examples on my blog.

Bjørn

A 3-D prism map can reveal patterns not so easily discovered in a traditional choropleth or a bar chart.

Which assumes that readers can see the baseline, which is not likely for a landlocked country. If you care at all about showing actual values and ratios, you have to give up the paradigm of charting values on a map/globe, and placing values into something like a bar chart. Use a chloropleth to show people the geographic relationships (that is, to show regional effects that encompass multiple countries), then use a bar chart with data sorted by a meaningful factor (by value of the target or other variable, not by spelling of country name).

From Slocum et al., 2005 (“Thematic Cartography and geographic visualization”), page 70:

“Use of perspective height produces what is commonly termed a prism map. In Figure 4.11 note that perspective height is the only visual variable receiving a “good” rating for numerical data. The justification is that an unclassed map based on perspective height can portray ratios correctly (a date value twice as large as another will be represented by a prism twice as high), and that readers perceive the height of resulting prisms as ratios.”

Slocum recommends lightness and hue as visual variables for nominal and ordinal data, and perspective height for numerical data (ratios).

After reading this statement:
“At least, the dome shape makes it possible to calculate the volume of each object, as the volume should represent the statistical value.”

Your statement did not clarify that you meant is is possible for the computational software to calculate the size of a bubble based on a value. It reads as if the already displayed dome shape is easy for people to calculate its volume.

I said this:
“Bjørn reminds us that the 3D prisms make country comparison easier when spinning the globe.”

After reading this:
“I’m using two visual variables (colour and height) to represent the same statistical indicator. This makes country comparison easier when spinning the globe.”

On re-reading your statement, I see that the different colors makes it possible to make sense out of the prism heights. Which again raises the question:

If you have two display features (color and prism height) which encode the same variable, and one of these is difficult to interpret (the prism heights), why not use a single feature which is easy to read?

You’ve admitted in several statements that the prism construction has shortcomings in terms of comprehensibility, and you have not satisfactorily explained what advantages it has. So the only reason I can think of to persist in using these is that you’ve develped a technology (in search of a problem) and are looking for problems that it helps to address. So far you have been looking unsuccessfully, since the basic chloropleth is superior.

Thanks for joining the discussion. A few clarifications from my side:

“Bjørn assures us that the dome shape allows people to judge their volumes.”

Wrong. I’m only saying that volume of each symbol are calculated according to a statistical value. I do acknowledge that people are not particularly good at estimating volumes, especially when seen in perspective. It’s one degree harder for the viewer to assess the relative size of 3-dimensional symbols compared to 2-dimensional, which again is harder to compare to 1-dimensional.
http://blog.thematicmapping.org/2008/06/why-3d-is-not-working-4-is-it-only-eye.html
http://blog.thematicmapping.org/2008/06/proportional-symbols-in-three.html

“Bjørn reminds us that the 3D prisms make country comparison easier when spinning the globe.”

Wrong. I’ve said that the ability to compare all countries is lost when thematic maps are rendered on a globe. Still there are various ways to address this issue:
http://blog.thematicmapping.org/2008/06/why-3d-works-1-looking-on-other-side.html

good post here.

I just read a new report from Akamai tittled “The State of the Internet”. Link: http://www.akamai.com/stateoftheinternet/

On this page, it has some flashy heatmap maps covering all the continents.

If you download the Q4′2008 report, on the 2nd page (where the globe ’shines’), the caption stated this “The “spinning globe” featured in the Akamai NOCC represents where Akamai servers are located and how much traffic they are seeing.”

Again, nice to look, but hard to digest the data ;)