## Nov 13, 2009

### Make a US county thematic map using Mathematica

I read a blog entry How to Make a US County Thematic Map Using Free Tools. The idea is to use Python script to modify the style settings in SVG file to make the most recent unemployment map. Mathematica can’t import SVG file directly, however, SVG file is in XML format, it is very easy to extract the necessary data from SVG file. If you are not sure what’s going here, please refer to the original blog.

All the files are zipped together, just unzip it, run the notebook. Download it here.

## Nov 2, 2009

### User-defined color themes

With Blend function, it is quite simple to use user-defined color themes.

Blend[{col1, col2, col3, ...}, x]: linearly interpolates between colors coli as x varies from 0 to 1.

We like to use the following color theme:

c = {{37, 57, 175}, {40, 127, 251}, {50, 190, 255}, {106, 235,
255}, {138, 236, 174}, {205, 255, 162}, {240, 236, 121}, {255,
189, 87}, {255, 161, 68}, {255, 186, 133}, {255, 255, 255}};

colors = RGBColor[#/255] & /@ c;

This shows the each color in the theme:

Graphics[Table[{EdgeForm[Black], FaceForm[colors[[i]]],
Rectangle[{i, 0}, {i + 1, 1}]}, {i, 1, Length[colors]}]]

Check the color theme with Blend function:

DensityPlot[x, {x, 0, Length[c]}, {y, 0, 1}, AspectRatio -> Automatic,
FrameTicks -> None, ColorFunction -> (Blend[colors, #] &),

Then you probably notice how to use it in your own plot,

ColorFunction -> (Blend[colors, #] &)

Test the color theme with the data:

ReliefPlot[data, ColorFunction -> (Blend[colors, #] &)]

Maybe the ligher color is better.

lightercolors = Lighter[#] & /@ colors;

Just for fun, let’s play the color theme with an existing image.

img=ImageData[ColorConvert[place_any_image_here, ”Grayscale”]];

ArrayPlot[img, ColorFunction -> (Blend[darkercolors, #] &)]