You can do calculations, but you’ll need to pass the resulting value to the template. There are two ways to do this:
1) Calculate the value when a post is saved (using the WP ‘save_post’ action). Store the result in a custom field. Then, you can display the custom field in the template.
2) There’s a MapPress filter to do these calculations whenever the map is displayed. This should get you started if you want to take that approach: