## Dec 7, 2008

### Tip: create 3D Map

Here is a simple explanation on how to create 3D map in the previous post.

The key is to use Extrude function (I copied it somewhere):

extrude[pts_, h_] := Module[{vb, vt, len = Length[pts], nh},
If[! NumericQ[h], nh = 0., nh = N@h];
vb = Table[{pts[[i, 1]], pts[[i, 2]], 0}, {i, len}];
vt = Table[{pts[[i, 1]], pts[[i, 2]], nh}, {i, len}];
GraphicsComplex[
Join[vb, vt], {Polygon[Range[len]],
Polygon[Append[
Table[{i, i + 1, len + i + 1, len + i}, {i, len - 1}], {len, 1,
len + 1, 2 len}]], Polygon[Range[len + 1, 2 len]]}]]

Let's create a map to show per-capita oil consumption in South America.

(* get the data *)

(* Falkland Islands is removed *)

mapdata = {First@CountryData[#, "Polygon"],
CountryData[#, "OilConsumption"]/
CountryData[#, "Population"]} & /@
DeleteCases[CountryData["SouthAmerica"], "FalklandIslands"];
mapdata[[All, 2]] = Rescale[mapdata[[All, 2]]];

(* 3D map *)

Graphics3D[{EdgeForm[Darker[ColorData["Rainbow"][#[[2]]]]],
FaceForm[ColorData["Rainbow"][#[[2]]]],
extrude[#[[1, 1]], #[[2]]]} & /@ mapdata, Boxed -> False,
Lighting -> "Neutral", BoxRatios -> {1, 1, 0.2}, ImageSize -> 800]

The visual quality of 3D map is low, however, it is good enough for the classroom.