Smoothing data on one half

So, my problem is that I have a matrix with 3 columns and 64800 rows. The first column shows the longitude measured in degrees going from -179.5:179.5. The second column shows the latitude also in degrees going from -89.5:89.5. The third row shows a binary mask for Greenland. For every coordinate that is within Greenland the value is 1 and elsewhere the value is 0. I want to smooth the data so it is only smoothened away from the coast. Right now I have sorted the rows by row [1 2] and then smoothened the data and then sorted the rows by [2 1] and smoothened the data. My problem is, that the function smooth both away and onto the coast which means the total sum is remained. I want it to smooth outwards so that the sum gets larger by a factor I can choose.