Returning the "column" number of a Button Down function on an image (GUIDE)

Hello. I have an image loaded onto an axes component in GUIDe and I want the mouse location over the squares to drive an xystage to a positon

All I need to return is which column is selected when the mouse if over a particular square: i.e just considering 1D (i.e. columns), if after pressing the mouse, the x coordinate is between 13 & 39, then report column1 (or just 1). If the x coordinate is between 88 and 114, then report back 3. In reality I have 12 columns so am looking a) for the best way to do this, and b) the best way to define the edges (the values of which I have)

This is my mouse click function

   function mouse3Callback(src, eventData)
    handles = guidata(src);
    axesHandle=get(src,'Parent');   %Object handle is the image
    xyz=get(axesHandle,'CurrentPoint');        
    x = round(xyz(1,1))
    y = round(xyz(1,2))
    

that I assign to the axes holding the image (axes3) Button down fucntion:

    set(handles.axes3, 'ButtonDownFcn', @mouse3Callback),

Thnaks for any help

[Jason]

i've come with this, maybe there is a better way:

     LE=[15,62,109,157,204,251,298,345,391,438,484,531]  %Left egde
     RE=LE+32                                            %Right Edge
     col=0;
     for i=1:12
         if (x>LE(i)&&x<RE(i))
             col=i
         end
     end
     col
     set(handles.editPt,'String',num2str(col))