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First create global variables (in functions.php or as a mu-plugin):

<?php

/*
 * CUSTOM GLOBAL VARIABLES
 */
function wtnerd_global_vars() {

    global $wtnerd;
    $wtnerd = array(

        'edition'  => get_query_var('category_name'),
        'channel'  => get_query_var('channel'),
        'tag'      => get_query_var('tag'),

    );

}
add_action( 'parse_query', 'wtnerd_global_vars' );

Why are we using an associative array variable $wtnerd? Because global variables need to be unique, and by keeping $wtnerd unique we can have simpler names for all the variables in its array.

By the way, the same can also be done like this:

<?php

/*
 * CUSTOM GLOBAL VARIABLES
 */
function wtnerd_global_vars() {

    global $wtnerd;
    $wtnerd['edition'] = get_query_var('category_name');
    $wtnerd['channel'] = get_query_var('channel');
    $wtnerd['tag']     = get_query_var('tag');

}
add_action( 'parse_query', 'wtnerd_global_vars' );

Then use $GLOBALS[]; to call the variable elsewhere (another file):

<?php

if( $GLOBALS['wtnerd']['edition'] == uk ) {

    // Do something

}

If the function in which you are defining the global variables is not hooked into a filter or action, e.g. add_action( 'parse_query', 'wtnerd_global_vars' ); as we are doing above, then you should do it as shown below.

In functions.php or mu-plugin:

<?php

/*
 * CUSTOM GLOBAL VARIABLES
 */
function wtnerd_global_vars() {

    global $wtnerd;
    $wtnerd = array(

        'edition'  => get_query_var('category_name'),
        'channel'  => get_query_var('channel'),
        'tag'      => get_query_var('tag'),

    );

}

Then, to call the variable elsewhere (another file), you need to manually initialize the function before you can use the variable:

<?php

wtnerd_global_vars();
if( $GLOBALS['wtnerd']['edition'] == uk ) {

    // Do something

}