Finding the outline of part of a matrix

I have a 2D matrix of latitude and longitude coordinates that I have used to create a mask. The mask is comprised of NaNs and 1s, depending on if the grid box is included in my mask.

What I want to do is find the coordinates of the boundary of this mask, so that I can plot a line around the shape designated by the 1s.

For example:

NaN NaN NaN NaN NaN

NaN  1   1  NaN  1

NaN  1   1   1   1

NaN NaN NaN  1  NaN

How do I draw a line around the shape seen in the 1s, and save the coordinates of this line so that I can overlay it in other plots?

I've tried using contour, but it gives diagonal lines, where I only want horizontal or vertical lines.

I found this thread http://www.mathworks.com/matlabcentral/newsreader/view_thread/304168 but I wasn't able to follow the solution.

Any help would be greatly appreciated.

[the cyclist]

What, precisely, do you want the output to be, when the input is the matrix you gave us?