How to plot a 2D arena firing field?

Hello all! I'm a researcher in neuroscience and I'm working on firing rates on a 2D linear arena. This is basically a square shaped arena with a whole in the middle so the rat follows a linear square-shaped path. I have already the values of firing rates for each position, but now I'd like to display it as a linear plot starting from a reference point. I'm struggling with this becuase distance calculation (which would be the simplest) is not a good approach since we have 2 different points at the same distance of the reference point. My idea was to crop the square into 4 different sides, and loop around them. However I've been working a couple of days on this and no result so far. I've been using image processing toolbox. Any clues on how could I loop around the hollow square and extracting the firing rates values? Thank you so much!

[Image Analyst]

Do you have a path that consists of the (x,y) location and a firing rate for when the rat is at that location? Attach a diagram to help illustrate your setup.