map appear is white

Hi everyone and good day,

I'm stuck when the contourm code doesn't work to colour my map (see image below).

Can someone help me?. Here is my command script:

>> ncdisp('https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdHadISST')

>> time = ncread('https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdHadISST','time');

>> time_ymdhms = datevec(time/86400 + datenum([1970 1 1 0 0 0]));

>> lat = ncread('https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdHadISST’,'latitude');

>> lon = ncread('https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdHadISST','longitude');

>> lon_aoi = find(lon >= 70 & lon <= 100);

>> lat_aoi = find(lat >= -20 & lat <= 0);

>> time_aoi = find(time_ymdhms(:,1) == 2009 & time_ymdhms(:,2) == 1);

>> aoi_start = [lon_aoi(1) lat_aoi(1) time_aoi(1)];

>> aoi_span_year = [length(lon_aoi) length(lat_aoi) 12];

>>sst_year=ncread('https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdHadISST’,'sst',aoi_start,aoi_span_year);

>> med_sst = nanmedian(sst_year,3);

>> figure

axesm('mercator','MapLatLimit',[-20 0],'MapLonLimit',[70 100],'MeridianLabel','on','ParallelLabel','on','MLabelLocation',70:2:100,'PLabelLocation',-20:2:0,'MLabelParallel','south');

>> contourm(lat_aoi,lon_aoi,med_sst','fill','on','LevelStep',0.01);

>> title(sprintf('Monthly SST %s - %s', datestr(time_ymdhms(time_aoi,:),'mmm-yyyy'),datestr(time_ymdhms(time_aoi+11,:),'mmm-yyyy')));

>> colormap(jet);

>> caxis([25 30]);

>> c = colorbar;

>> c.Label.String = 'SST (degree)';

>> geoshow('landareas.shp','FaceColor',[0.5 0.5 0.5]);

>> tightmap

Answer 1

[Bhanu Prakash]

Hi Noorashiekin,

I understand that you want to know why the map acquired is white even though you have used the ‘FaceColor’ argument, in ‘geoshow’ function, to colour the map grey.

The reason for the map being white is because of the latitude and longitude limits, which are (-20,0) and (70,100) respectively. For the limits provided, the contour plot is accurate.

To gain a better understanding of how a contour plot varies with different limits, consider the following code snippets:

%setting the limits 
worldmap([-20 0],[70 100]) 
%plotting the map data 
geoshow('landareas.shp','FaceColor',[0.5 0.5 0.5]) 

To obtain a different contour plot, you can change the limits as follows:

%setting the limits  
worldmap([-40 30],[50 160]) 
%plotting the map data 
geoshow('landareas.shp','FaceColor',[0.5 0.5 0.5]) 

To set the latitude and longitude limits, you can use the ‘worldmap’ function in MATLAB. For more information on the ‘worldmap’ function, refer to the following documentation:

https://in.mathworks.com/help/map/ref/worldmap.html