passing a value from page to page using routing concept

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C#

ASP.NET

Hi,

I have a global.asax class file where I am placing the seo url routing concept like this:

private static void RegisterRoutes(RouteCollection routes)
    {
        //More info about url routing http://www.codeproject.com/Articles/77199/URL-Routing-with-ASP-NET
        routes.MapPageRoute("", "", "~/Default.aspx");
        routes.MapPageRoute("", "{categorySEOName}", "~/Pages.aspx");
        routes.MapPageRoute("", "{categorySEOName}/{subcategorySEOName}", "~/Pages.aspx");
    }

and this how I am getting the data from database and rewrite my url:

public void LoadMenu()
   {
       CategoryInfo _CateogyInfo = new CategoryInfo();
       SubCategoryInfo _SubcateoryInfo = new SubCategoryInfo();
       List<CategoryInfo> categoryList = _CateogyInfo.GetCategory().ToList<CategoryInfo>();
       StringBuilder sb = new StringBuilder();
       string appname = Request.ApplicationPath == "/" ? "" : Request.ApplicationPath.ToString();
       sb.Append("<ul id='nav'>");
       foreach (CategoryInfo category in categoryList)
       {
           string seourl = string.Format("{0}/{1}", appname, category.CategorySEOName);
           sb.Append("<li><a class='hsubs' href=" + seourl + ">" + category.CategoryName + "</a>");
           _SubcateoryInfo.CategoryId = category.CategoryId != null ? category.CategoryId : 0;
           _SubcateoryInfo.CategoryId = Convert.ToInt32(Request["categoryId"]);
           List<SubCategoryInfo> SubcategoryList = _SubcateoryInfo.GetSubCategoryByCategoryId().ToList<SubCategoryInfo>();
           if (SubcategoryList.Count > 0)
           {
               sb.Append("<ul class='subs'>");
               foreach (SubCategoryInfo subCategory in SubcategoryList)
               {
                   seourl = string.Format("{0}/{1}/{2}", appname, category.CategorySEOName, subCategory.SubCategorySEOName);
                   sb.Append("<li><a href=" + seourl + ">" + subCategory.SubCategoryName + "</a></li>");
               }
               sb.Append("</ul>");
           }

       }
       sb.Append("</ul>");
       MenuSubMenu.Text = sb.ToString();
  }

Now my kestion is how can I get a categoryId requested by the user to pass it from page to page.
Like once a user click on category I want to get that categoryId and pass it as the request["CategoryId"] to my next page.

This is the way I used to get the requested Id :

app.Context.RewritePath("~/Category.aspx?Id=" + url[url.Length - 2] + "&name=" + url[url.Length - 1].Replace(".aspx", "") + "&type=category");

Now If I want to get the Id requested I will pass it to a variable like this:

_SubCategoryInfo.CategoryId = Convert.ToInt32(Request["Id"]);

But as u know this is not seo friendly.
Now I want to use the same idea to get the requested Id using routing concept.