Where does page live in site structure? and relative paths from that page

my first post. 🙂

I am wondering how to determine the relative path from a page I’ve created via WordPress interface to somewhere else in my site structure. That is, where is that page in my site’s directory tree? So I can create relative path from that page to content that is not in the WP database. Specific example follows…

I know there are some reasons not to use relative URLs, but in this case I have.

I have a page with some custom content. The assets are in a directory called “my-assets”, which is in the site’s html directory. For example:

mysite.com
__ / html
_____ / wp-content
_____ … other files and folders …
_____ / my-assets
_______ / clients-assets
__________ / css
__________ / images
__________ / etc
_______ / other-assets

I was uncertain how to path to the content from the page – page is a normal WP page, created from the Pages interface. I took a guess that pages reside at same level as index.php, inside /wp-content, so set a path relative to that location. It worked.

For example,

<img class="third" src="../my-assets/clients-assets/images/photos/sanfrancisco/209x171/209by171-1.png">
places an image, and

<link rel="stylesheet" href="../my-assets/clients-assets/css/clients.css">
loads the required stylesheet.

Great, it seemed I know where my path originates, so can link to any file from the page.
However I tried connecting to same content as if my page were at the root level of the html directory (not in wp-content). Like so…

<img class="first" src="/my-assets/clients-assets/images/photos/sanfrancisco/249x150/249by150-3.png">

<link rel="stylesheet" href="/my-assets/clients-assets/css/clients.css">

No “..” before “/my-assets/” and it still worked. Image loaded, stylesheet loaded.

Both can’t be right, can they? Is WP correcting the path that’s in error?
So what is the proper relative url from a WP-generated page? From the page to the site root for example. That is, where does the page reside? Do I set that somewhere or is it a constant?

Much thanks for any help with this question.