Best URL structure for big site

[mdshowketull]

Hi Folks,

I was wondering if anyone can suggest what way URL structure should be constructed for best practice.

My Current setup:

Home Page>Location(Available List of Product Groups Name)>Product Page(group of Product)
Contact US
T&C
About US

We have over 20 Locations 
Each location has over 70 product Group. all product Group page tagged with chronical as duplicate Group possible in different areas.
Each Product Group has more than 100 Products. all listed in same page.

Currently my site map is indexed :
Home Page
Home Page>Location(Available List of Product Groups Name)   : around 20 page
Contact US
T&C
About US


Site map doesn't include all my Product Group page. Is there a batter way to structure this when SEO is mind? 
Thanks in Advance.