Embedding Templates in the Header File Based On Categories - html

Question

I am using ExpressionEngine 2.2.1 and am trying to create a conditional that will cause a page to show a specific navigation template based on the page's category. For example, I am creating a public profile for someone who is a part of a competition in London. When someone visits his profile, I would like the page to show, not only his profile, but also a banner with an image of London & navigation that is specific to the London competition. I would like to do this by adding a conditional with categories since we have so many competitors in many different cities. I have created a category titled "London Competitors English" and it has the ID of "56". Once I have created the competitor's profile within EE, I select the category, "London Competitors English," however, when I go to the page, the default navigation template is loading rather than the London template. I created code based on my research and most related example here: http://expressionengine.com/forums/viewthread/185555/. What do I have wrong in my code?:
FILE ONE: (condensed portion of) competitor_profiles_en/index.html where "competitor_profiles_en" is the template:
{exp:channel:entries limit="1" url_title={segment_2} }
{embed="includes/header"}
<div class="xx">
<h2>{competitor_first_name}<br>{competitor_last_name}</h2>
...
</div>
{/exp:channel:entries}
FILE TWO: (condensed portion of) my header.html file :
{if segment_1 == 'home'}
{embed="includes/_nav_landing"}
{if:elseif "{categories}{category_id}{/categories}" == "56"}
{embed="includes/_nav_city_lon_en"}
{if:else}
{embed="includes/_nav_internal"}
{/if}

Answer 1

The problem is that embeds are processed after all other tags, in a completely separate process. So when your includes/header embed runs, it has no categories to speak of, because it's not actually running within a Channel Entries tag.
Unless you need to pass variables to includes/header (which you don't appear to be doing here, but you may have removed that for simplicity), I'd move your includes/header to a snippet instead, so it will be processed inline with your Channel Entries tag.

Answer 2

Derek's answer was spot on, and I would like to elaborate on my method of putting his suggestion into action.
I found information about snippets here http://expressionengine.com/user_guide/templates/globals/snippets.html and watched this tutorial here http://www.youtube.com/watch?v=AEEudo0BrRA&feature=related. I then created a snippet within the control panel (Design > Templates > Snippets) that included all of the code that was in the header file and titled it snippet_header_en. Because ExpressionEngine includes snippets as a part of the template that they are in, EE recognized my conditional including the categories that I created. Here is the revised code:
FILE ONE: (condensed portion of) competitor_profiles_en/index.html where "competitor_profiles_en" is the template:
{exp:channel:entries limit="1" url_title={segment_2} }
{snippet_header_en}
<div class="xx">
<h2>{competitor_first_name}<br>{competitor_last_name}</h2>
...
</div>
{/exp:channel:entries}
FILE TWO: (condensed portion of) my header.html file :
As previously mentioned, I moved this code to the snippet section of the EE control panel.