How can I change the color of a map given shapefile and values?

Hello, I would like to generate a map from shapefiles given where for each provinces I have a specific value. Let say I have 52 provinces, so I have an array of 52 different values. What I am doing now is to generate a loop:

for i = 1:52
  col_=cols(I(s),:);
  mapshow(obj.shapes(s),'FaceColor',col_);
end

How can I generate "I" and have a colorbar that indicates the real values? Now I am able to generate something like this but it is not what I want.

All the best.

Answer 1

[Nitin Khola]

As per my understanding, you wish to change the 'FaceColor' of polygons depicting provinces, as per some particular data values, which can be displayed using "mapshow" or "geoshow". Further, I understand that you are importing a shapefile containing the necessary information.

One of the possible methods to do this is by making a rule for the 'Polygon' geometry using " makesymbolspec " function.

A step by step procedure to do it is described in the following example:

Create Choropleth Map of Population Density

The sections most relevant to you are:

Create an autumn colormap for the six New England states, and then use the flipud command to invert the matrix.

fall = flipud(autumn(numel(NEstates)));

Make a symbol specification structure, a symbolspec , that assigns an autumn color to each polygon according to the population density.

densityColors = makesymbolspec('Polygon', {'PopDens2000', ...
   [0 maxdensity], 'FaceColor', fall});

This example creates an "autumn" colormap to display population density data. However, as stated in the example, you can experiment with other colormaps as well. You can also create a custom colormap.

For more information on using colorbars and colormaps in regard to representing geographic variables on maps, refer to the following documentation:

Using Colormaps and Colorbars

Answer 2

[Navid Ghajarnia]

As far as I understood, you can't do it in an easy way. But there is a way around it:

Lets imagine you want the hot colormap and you want 256 colors in it. so 1st step:

cmap = hot(256);

Then, lets imagin your data based on which you want to give color to your polygons is between 1 to 150. This means that if your province's value is one, then cmap(1,:) is your color and if your province's data is 150 then cmpa(256,:) gives you the final color in hot colormap. This means that with the command below you can get colors in a relatively continous way for each of your provinces:

color_row = round(Data/150 * 256);
cc = cmap(color_row,:);

Then by having the color code (cc) you can use mapshow and map your polygon and give the correct color to it.

Hope it helps...