Loop over lat and lon and convert them into a row or column, then assign the value, maybe like
maxCols = ceil(max(100 * lon));
maxRows = ceil(max(100 * lat));
rainfallImage = zeros(maxRows, maxCols, 'uint8');
for k = 1 : length(lat)
col = round(100 * lon(k));
row = round(100 * lat(k));
rainfallImage(row, col) = Rainfall(k);
end
imshow(rainfallImage, []);
colormap(hot(256));
colorbar;
imwrite(rainfallImage, 'RainFallImage.tif');
