# contourm plotting

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ash salut am 17 Mär. 2012
Beantwortet: Sanchari am 25 Jul. 2024 um 1:56
I have a text file containing Lats and Lons. I want to plot a geomap with 0.1 deg grid. Then the map use a color bar, showing the number of occurrences of the Lats and Longs.
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### Antworten (1)

Sanchari am 25 Jul. 2024 um 1:56
Hello Ash,
To plot a geomap with a 0.1-degree grid and use a color bar to show the number of occurrences of the latitude and longitude points from a text file, please follow these given (high-level) steps in MATLAB:
1. Read the data from the text file.
2. Create a grid with 0.1-degree resolution.
3. Count the occurrences of latitude and longitude points in each grid cell.
4. Plot the data on a geomap with a color bar.
Here's a complete example:
% Read the data from the text file
lats = data(:, 1);
lons = data(:, 2);
% Define the grid resolution
gridResolution = 0.1;
% Create the grid
latEdges = min(lats):gridResolution:max(lats);
lonEdges = min(lons):gridResolution:max(lons);
% Count occurrences in each grid cell
occurrences = histcounts2(lats, lons, latEdges, lonEdges);
% Create a figure
figure;
% Create a map with the specified grid resolution
latCenters = latEdges(1:end-1) + gridResolution/2;
lonCenters = lonEdges(1:end-1) + gridResolution/2;
% Plot the data using pcolor
pcolor(lonCenters, latCenters, occurrences);
colorbar;
xlabel('Longitude');
ylabel('Latitude');
title('Number of Occurrences of Lats and Lons');
% Optionally, use geoscatter for a more geographic visualization
% figure;
% geoscatter(lats, lons, [], occurrences(:), 'filled');
% colorbar;
% title('Number of Occurrences of Lats and Lons');
This code will create a geomap with a color bar indicating the number of occurrences of each latitude and longitude point within the specified grid cells.
Notes:
• Ensure that the text file "latlon.txt" is in the correct format and located in the current working directory or provide the full path to the file.
• Adjust the "gridResolution" if there is a need of different resolution.
• The "pcolor" function is used for plotting the grid data. If one prefers a geographic scatter plot, one can use "geoscatter" as shown in the commented section.
One can find more examples in the MathWorks Documentation for "contourm": Thematic Maps — Examples (mathworks.com)
Hope this helps!
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