# A good divergent color palette for Matlab

#### INTRODUCTION

Before starting my series on perceptual color palettes I thought it was worth mentioning an excellent function I found some time ago on the Matlab File Exchange. The function is called Light and Bartlein Color Maps. It was a Matlab Pick of the week, and it can be used to create four color palettes discussed in the EOS paper by Light and Bartlein. Each of these palettes is suited for a specific task, and the authors claim they are non confusing for viewers with color vision deficiencies.

In the remainder of this post I will showcase one of the palettes, called orange-white-purple, as it is good divergent scheme [1]. With the code below I am going to load the World Topography Matlab demo data, create  the palette and use it to display the data.

```%% load World Topography Matlab demo

%% create Light Bartlein orange-white-purple diverging scheme
LB=flipud(lbmap(256,'BrownBlue')); % flip it so blue is for negative(ocean)
% and green for positive (land)

%% plot map
fig2 = figure;
imagesc(flipud(topo));
axis equal
axis tight
axis off
set(fig2,'Position',[720 400 980 580]);
title(' Non-symmetric divergent orange-white-purple palette','Color',...
'k','FontSize',12,'FontWeight','demi');
colormap(LB);
colorbar;```

And here is the result below. I like this color scheme better than many othera for divergent data. One only issue in the figure, although not inherently due to the palette itself [2], is that the centre of the palette is not at the zero. This is a problem since the zero is such an important element in ratio data, in this case representing sea level.

#### MAKING THE PALETTE SYMMETRIC AROUND THE ZERO

The problem fortunately can be easily fixed by clipping the data limit to a symmetric range. In Matlab this has to be done programmatically, and rather than going about it with trial and error I like to do it automatically with the code below:

# Compare lists from text files using Matlab – an application for resource exploration

#### INTRODUCTION

With today’s post I would like to share a Matlab script I used often to compare lists of ID numbers stored in separate text files. The ID numbers can be of anything: oil and gas wells, mining diamond drill hole locations, gravity or resistivity measurement stations, outcrop locations, you name it. And the script will handle any combination of ASCII characters (numbers, letters, etcetera).

I included below here some test files for you to try with the code, which is in the next section. Please refer to the comment section in the code for usage and file description. Have fun, and if you try it on your lists, let me know how it works for you.

#### TEST FILES

These files are in doc format; they need to be downloaded and saved as plain txt files. Test1 and Test2 contain 2 short lists of (fake) Canadian Oil and Gas wells; the former is the result of a search using a criterion (wells inside a polygonal area), the latter is a list of wells that have digital wireline logs. Test3 and Test4 are short lists of (fake) diamond drill holes.

*** Notice that script is setup to compare list in Test2.txt against list in Test1.txt and not the other way around. If using this on your own lists, you will have to decide in advance which subset of wells you are interested in.

Test1

Test2

Test3

Test4

#### THE SCRIPT

Here is the code: