How to update field values of a content type's nodes when when viewing a particular content type page I'd essentially like to alter the values of a specific custom field of a few of nodes before they're displayed in a view on the 'page' of a specific content type.

The content type is that will be displayed is a park. When a park is viewed, one of the blocks shown is a view that fetches and shows several nodes that are also 'parks'. 

This park content type has a field called proximity. I'd like to change the value of proximity (based on a mathematical formula) for all parks before the view is processed, so that I can use proximity in the view.

From what I understand so far, I should use a park_preprocess function, which calls some sort of hook to change the proximity values. Is this correct, and how would I do it?
hook_node_view() will be used in this scenario.

function hook_node_view($node, $view_mode, $langcode) {
  if($node-&gt;type == 'park' &amp;&amp; $view_mode == 'full')
   {
    /* change the value of proximity here after applying your formula. 
      * Here you have complete node array, so you alter the result easily here.
    */

   }
 }