visualization: The Age of Homes

Following is an interesting visualization map, but it could be misleading
because of using random color to represent ranges of values...
Big data needs smart visualization techniques... but what is a good way?

The Age of Homes in All 50 States | Zillow Blog
"...single-family houses built from 1900 to 2014 to see which decades are most represented by the current housing stock..."


I.e., what is a good way to color-code ranges of values on a chart or a map?

Diverging Color Maps for Scientific Visualization

... mapping scalar values to colors... allows us to view scalar fields by coloring surfaces and volumes. ... rainbow color map... which naively sweeps through the most saturated colors, is well known for its ability to obscure data, introduce artifacts, and confuse users.

Vis Lies 2013 – The Blog of Dr. Moron

 bad vs. good  

Based on this observation, next visual map is still not optimal,
while better than just using random colors as on the first map. 

Climate Map | Meandering Through Mathematics

elections are a typical example of using color-maps. 

In that case two main colors are easy choice, 

but different population density creates another challenge: 

colored surface not proportional to number of values. 

Geographical hotspot analysis for election data | The SAS Training Post

A better way is to utilize "bubble map"

Here is one example from Microsoft "Power Map" reporting tool. 

Better, but still not perfect. 

Microsoft Power Map | Reporting content from SQL Server Pro

In all, color map visualization challenge appears to be not solved still. 

If there is a good solution, it is hiding well from Google :)