I released a new version of the Thematic Mapping Engine today as a response to this discussion. The most noticeable new feature is the enhanced colour scale. It's difficult to make a symbol legend in KML, as symbol size varies with scale (zoom). Without a legend, it's very hard to assess the exact values.
This is why I duplicate symbology by supporting a colour legend. You can now easily define a colour scale for all thematic mapping techniques. The colour legend informs the user about the range of values (min and max), and where the different symbols are positioned on this range.
The colour scale can be unclassed or classed:
- Equal intervals: Each colour class occupies an equal interval along the value range.
- Quantiles: The countries are rank-ordered and equal number of countries are placed in each colour class. Quantiles are not available for time series.
Here is a few examples (all statistics from UNdata):
Eye candy: Mobile phone subscribers, 2004 (unclassed).
Try it yourself!