Dealing with thematic maps, how to read a shapefile and giving him an additional data array

Hello to everybody, i'm trying to learn how to build rapidly a thematic map of several parameters that i have to represent but, following the guidelines (<http://www.mathworks.it/it/help/map/thematic-maps-1.html>) i could not get totally the point. This is the matter: i have to represent with a thematic map the variation of the Production Price of the Wheat across the world in 2011. First of all i have loaded a shapefile of the world (that is TM_WORLD_BORDERS-0.3.shp). It has all the informations to create a map of the world and to recognize the boundaries of the nations.

world=shaperead('TM_WORLD_BORDERS-0.3.shp')

By reading the suggestions in the tutorial it has been easy to make a thematic map according to one of the parameters that is already inside the shapefile (the shp has already inside NAME AREA POP2005 REGION SUBREGION LON LAT) by using

maxdensity = max([world.POP2005]);
fall = flipud(autumn(numel(world)));
densityColors = makesymbolspec('Polygon', {'POP2005',[0 maxdensity], 'FaceColor', fall});
geoshow(world, 'DisplayType', 'polygon','SymbolSpec', densityColors)
title ({'density population of nations in 2005'})

but i did not understand how to arrange a thematic map according to a column array coming from outside the shapefile . for example, the production price that i have just downloaded from FAOSTAT website.

thanks a lot

Answer 1

[Kelly Kearney]

If you're comfortable with the geoshow/symbolspec combo, the easiest way to do this would be to add your additional data as new fields to the structure:

pth = '~/Documents/Research/Data/TM_WORLD_BORDERS-0.3/'; % change as appropriate

world = shaperead(fullfile(pth, 'TM_WORLD_BORDERS-0.3.shp'), 'usegeocoords', true);
mystat = num2cell(1:246);
ss = makesymbolspec('Polygon', {'mystat', [1 246], 'facecolor', jet(64)});
[world.mystat] = deal(mystat{:});
geoshow(world, 'DisplayType', 'polygon','SymbolSpec', ss);

[Alessandro]

yes, actually it has worked! since i do not have all the values of each country in the list, is there a possibility to set the coulour white for the nations that have a NaN value in their position?

[Kelly Kearney]

It falls back on the default color for NaN values (which is a light yellow if you don't change anything), so you just need to change that.

cmap = jet(64); % Or whatever colormap you prefer
clim = [1 246]; % Or color limits match your data

ss = makesymbolspec('Polygon', ...
    {'mystat', clim, 'facecolor', cmap}, ...
    {'Default', 'facecolor', 'w'});

[Alessandro]

Also another trick i would like to know is how to decide the boundaries of each color in the color map: since in the thematic map i cannot ignore the outliers (for ex all the values around 2 and some outlier is 50) i would like to indicate by myself which are the colours and the range values of every colour. thank you

[Kelly Kearney]

The clim option in my example controls the range of values that correspond to the colormap. Quite honestly, I've always found the makesymbolspec + geoshow approach to be unnecessarily complicated. You may be better off plotting the data via patchm if you have a lot of these specific colormapping requirements. That way, the colors of the patches can be specifically linked to the figure colormap. And it's certainly a lot easier to change things later using patchm:

pth = '~/Documents/Research/Data/TM_WORLD_BORDERS-0.3/'; 
world = shaperead(...
  fullfile(pth, 'TM_WORLD_BORDERS-0.3.shp'),'usegeocoords', true);
mystat = randn(size(world));

axesm('pcarre');
for ii = 1:length(world)
    hp(ii) = patchm(world(ii).Lat, world(ii).Lon, 'r');
end
set(hp, {'cdata'}, num2cell(mystat));
set(hp, 'facecolor', 'flat');
set(gca, 'clim', [-2 2]);

[Alessandro]

Actually i would prefer to continue using the old way, at least to have all the graphs drawn in the same way! as you can see below, i've managed to define the colour boundaries according to the values but there is a scam: i think that, even if i'm setting the colour boundaries, the colorbar is doing on its own and it is not considering them but only the minimum and the maximum limits. This would be a problem because i would like to have lots of colours for the range value going from 0 to 1000 and one colour describing values from 1000 to MAX (outliers), instead colourbar divides the color range in an equal way.

pth = '/Users/macbook/.../TM_WORLD_BORDERS-0.3/'; 
mapworld = shaperead(fullfile(pth, 'TM_WORLD_BORDERS-0.3.shp'), 'usegeocoords', true);
mapdatas = num2cell(Cln);
MAPmaxdensity = max([Cln])
mapss = makesymbolspec('Polygon',...
{'mapdatas', [0 150], 'facecolor', [0 0 255]},…
{'mapdatas', [150 250], 'facecolor', [153 203 255]},…
{'mapdatas', [250 350], 'facecolor', [153 255 204]},…
{'mapdatas', [350 550], 'facecolor', [0 255 0]},...
{'mapdatas', [550 1000], 'facecolor', [255 0 0]},...
{'mapdatas', [1000 MAPmaxdensity], 'facecolor', [255 36 0]},...
{'Default', 'facecolor', 'w'});
[mapworld.mapdatas] = deal(mapdatas{:});
caxis([0 MAPmaxdensity])
colormap(jet(8))
colorbar
geoshow(mapworld, 'DisplayType', 'polygon','SymbolSpec', mapss)
title ({''})

If i could solve the problem of colorbar would be easy also to represent logarithmic values, thanks for the help.

[Rolando Gonzales Martinez]

I was looking for this answer for hours. Thanks from 2021, Kelly!