Saturday 21 June 2008

What a colourful world

3D thematic mapping can be challenging, and I've been considering some of the problematic issues in a series of blog post (1, 2, 3, 4). There has also been a discussion on the CartoTalk forum, and Rich Treves posted a response on his blog.

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):

Life expectancy at birth, 2005 (equal intervals).

Life expectancy at birth, 2005 (quantiles).

Aids estimated deaths, aged 0-49, 2005 (equal intervals).

Eye candy: Mobile phone subscribers, 2004 (unclassed).

Try it yourself!

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