Analyze and Visualize Geographic Information with MATLAB

Any data which you refer to in terms of real-world coordinates that are longitude and latitude (projected) or in unprojected map, is called georeferenced data. Georeferenced data is also known as spatial, geographical or geospatial data.

Type of Geo Data

There are two types of geo data vector geo data and raster geo data.

Vector Geo data

It consists of latitude & longitude(pairs) in a sequence or projected (x,y) coordinate pairs. To identify different objects or places or things, there must be break in data otherwise it will be considered as a single entity. For example if I have to locate two neighbour countries on map, there must be a space or a break in data to identify both countries exclusively. Vector data can be edges or coastline or points or polygon. As given below figure

Raster Geodata

Data will be in a matrix form, in which each row-and-column element corresponds to a geographical area or geographical information as patch( filled), along with that there will be a reference to locate that matrix or image data on geo coordinate system.

It can be two types

1. Digital Elevation that is topographical map with geographical reference.
2. Remotely sensed Images with geographical reference.

Geographic Data Import and Export / Standard File Formats in MATLAB

2D and 3D Map Displays

Before map Display we are to set projection on axes, there are more than 65 projections available in MATLAB

Map Projections

There are three main families

Cylindrical Projections

axesm ('balthsrt', 'Frame', 'on', 'Grid', 'on')
 plotm(coastlat,coastlon)

Conic Projections

axesm ('eqdconic', 'Frame', 'on', 'Grid', 'on');
plotm(coastlat,coastlon)

Azimuthal Projections

axesm ('gnomonic', 'Frame', 'on', 'Grid', 'on');
 plotm(coastlat,coastlon)

You can use your custom axis too with axesm by giving latitude and longitude limits. Or you can use worldmap command to get coordinate of a specific country.

worldmap India

2D Map Display

geoshow command is used for projected map and mapshow command is used for unprojected map

worldmap asia
geoshow('landareas.shp','FaceColor',[0.5 1.0 0.5]) 

R = geotiffinfo('year1.tif'); 
[A, R] = geotiffread('year1.tif'); %  A is a matrix, R is a Geo reference
geoshow(A,R)

3D Map Display

Define projection

figure
ax = axesm('globe');
ax.Clipping = 'off';
gridm('GLineStyle','-','Gcolor',[.1 .4 .4],'Galtitude',.03)

load coast data and plot it as red

load coastlines
plot3m(coastlat,coastlon,.01,'r')
view(3)
axis off
zoom(1.5)

Create matrix and Geo reference

matrix = ones(180,360);
reference = georefcells([-90 90],[0 360],size(base));

Plot above created raster data

copperColor = [0.4 0.6 0.8];
geoshow(matrix,reference,'FaceColor', [0.4 0.6 0.7] )
camlight headlight
material([.5 .6 .2])

Thematic Maps

Thematic maps are spatial variation of geographic distributions. These distributions may be physical phenomena such as atmosphere or ozone data or human data, such as census, diseases or agriculture data.

Get Image information and plot it

clear
R = geotiffinfo('year1.tif'); 
[A, Rr] = geotiffread('year1.tif');
geoshow(A,Rr)

Get x,y locations of pixels and plot surface

[x,y] = pixcenters(R); 
 h=surf(x,y,A)
view([-30,30])
%% set(h,'EdgeColor','none')
material([.5 .8 .1])
shading interp
% axis equal;
% demcmap(A)
lighting gouraud
view(40,56)
colorbar

Data Representation on MAP

You can use MATLAB functions, plotm, mapshow, geoshow, geobubble, or geoplot.

If you want to display data on live map ,you can use wmmarker

Visualization of Geo Data

Below code shows how you can plot different size of circles using geoplot

load coastlines.mat
a=1:numel(coastlat);
aa=rescale(a(1:length(coastlon)),1,20);
%geobasemap(colorterrain')
for i=1:100:length(coastlat)
geoplot(coastlat(i),coastlon(i),'o','MarkerSize',aa(i),'MarkerFaceColor','red')
hold on
text(coastlat(i),coastlon(i),string(aa(i')))
end
hold off
geobasemap('colorterrain')

Analysis and Visualization of Temperature Data

My data looks like as given below

Read Table

TempData=readtable("TempDataofIndia.xlsx");
sum(ismissing(TempData.Temp))
temp=TempData.Temp;

Fill Missing Temperature Data

You can use live script capability to fill missing data, to know click here for my previous post.

% Fill missing data
[CLeanedTemp,missingIndices] = fillmissing(temp,'spline');

% Display results
clf
plot(CLeanedTemp,'Color',[0 114 189]/255,'LineWidth',1.5,...
    'DisplayName','Cleaned data')
hold on

% Plot filled missing entries
plot(find(missingIndices),CLeanedTemp(missingIndices),'.','MarkerSize',12,...
    'Color',[217 83 25]/255,'DisplayName','Filled missing entries')
title(['Number of filled missing entries: ' num2str(nnz(missingIndices))])

hold off
legend
clear missingIndices
close all

Read Latitude and Longitude from table

Lat=TempData.Lat;
Lon=TempData.Lon;

Show India Map

To show states in different colors makesymbolspec function is used.

ax = worldmap('INDIA');
load coastlines
geoshow(ax, coastlat, coastlon,...
'DisplayType', 'polygon', 'FaceColor', [.45 .60 .30])
states = shaperead('INDIA', 'UseGeoCoords', true);
faceColors = makesymbolspec('Patch',...
    {'INDEX', [1 numel(states)], 'FaceColor', ...
    polcmap(numel(states))}); % NOTE - colors are random
geoshow(ax, states, 'DisplayType', 'polygon', ...
  'SymbolSpec', faceColors)

Show Places on Map As points

To display text data on map you can use textm, but in this case non-geographic text function is used.

geoshow(Lat, Lon,...
    'DisplayType', 'point',...
    'Marker', 'o',...
    'MarkerEdgeColor', 'r',...
    'MarkerFaceColor', 'r',...
    'MarkerSize', 3)

h1=text(-1.5120*10^6,4.7747*10^6,'District');
h2=text(-1.4969*10^6,4.6164*10^6,'Click on red point to know temperature');

Create Interactive app:- Click to know Temperature‘

while 1
    
    [selected_lat,selected_lon] = inputm(1)
   
    
    if isempty(selected_lat)
        break % User typed ENTER
    end
    d = distance(Lat, Lon, selected_lat, selected_lon);
    k = find(d == min(d(:)),1);

    geoshow(Lat(k), Lon(k), ...
        'DisplayType', 'point', ...
        'Marker', 'o', ...
        'MarkerEdgeColor', 'k', ...
        'MarkerFaceColor', 'y', ...
        'MarkerSize', 3)
    h1.String = {[TempData.District{k}]};
    h2.String = num2str([CLeanedTemp(k)],'%10.2f');
         
end

Webmap

You can display data on live map using webmap

wmmarker(Lat(100:120),Lon(100:120),'FeatureName',string(CLeanedTemp(100:120))) % plot temp 100 to 120 idx

Click here for recorded webinar to learn analysis and visulization of geodata