Regarding the contour matrix obtained from contourf

I recently ran contourf on the image below .

.

The output of this is as follows

Now when I plot the contour matrix for Number 240,I am getting something like this

Any ideas why there is a line in the middle of the contour,I know that the matrix returned from contourf is a 2xn matrix wherein the first column in each set contains the contour level and the number of vertices at that level.So what I did was from the original contour matrix I removed those columns where it mentions the contour level and the number of vertices at that level.

I also read somewhere that the inputs to contourf should be strictly increasing or decreasing,since the input image contains rows and columns not in strict increasing/decreasing order,do you think that could be one reason as to why there is a line in the middle of the 3rd plot.

Any help will be appreciated.

[KSSV]

This can be sorted. You need to add NaN at the end or arrange the points so thay you will get a closed region.

[Sparsh Garg]

I tried to sort them but that is not working

I have seen posts that mention NaN,but I have some question

for the example shown below

In this there are two lines starting at (29.69,10) ,one ends at (239,3) and the other at (239,205).

Could you please tell me how adding NaNs in the end will help in resolving the issue

Also if you could give me some suggestions on how to arrange the points in a closed region that will also help.

[KSSV]

Yes you will get like that....you eed to clean/ remove those data points.

[Sparsh Garg]

Thanks for the help KSSV,I replaced the points by NAN and that helps.