GeoIP functions for WordPress. Requires some external GeoIP files and .dat file from MaxMind.

functions.php

/*
 * Region Select Custom Post Type
 */
    function cutandrun2016_post_type() {

         // US editors
        $us_post_labels = array(
            'name'               => _x('US Region', ''),
            'singular_name'      => _x('US Region', ''),
            'add_new'            => _x('Add New', 'editor'),
            'add_new_item'       => __('Add New'),
            'edit_item'          => __('Edit'),
            'new_item'           => __('New'),
            'all_items'          => __('All'),
            'view_item'          => __('View'),
            'search_items'       => __('Search'),
            'not_found'          => __('Not found'),
            'not_found_in_trash' => __('Not found in the Trash'),
            'parent_item_colon'  => '',
            'menu_name'          => 'US Region'
        );
        $us_post_options = array(
            'labels'             => $us_post_labels,
            'description'        => '',
            'public'             => true,
            'menu_position'      => 5,
            'supports'           => array('title', 'editor', 'thumbnail', 'page-attributes'),
            'hierarchical'       => true,
            'capability_type'    => 'page',
            'show_in_menu'       => true,
            'show_in_nav_menus'  => true,
            'menu_icon'          => 'dashicons-admin-site'
        );
        register_post_type('us', $us_post_options);


        // UK editors
        $uk_post_labels = array(
            'name'               => _x('UK Region', ''),
            'singular_name'      => _x('UK Region', ''),
            'add_new'            => _x('Add New', 'editor'),
            'add_new_item'       => __('Add New'),
            'edit_item'          => __('Edit'),
            'new_item'           => __('New'),
            'all_items'          => __('All'),
            'view_item'          => __('View'),
            'search_items'       => __('Search'),
            'not_found'          => __('Not found'),
            'not_found_in_trash' => __('Not found in the Trash'),
            'parent_item_colon'  => '',
            'menu_name'          => 'UK Region',
        );
        $uk_post_options = array(
            'labels'             => $uk_post_labels,
            'description'        => '',
            'public'             => true,
            'menu_position'      => 5,
            'supports'           => array('title', 'editor', 'thumbnail', 'page-attributes'),
            'hierarchical'       => true,
            'capability_type'    => 'page',
            'show_in_menu'       => true,
            'show_in_nav_menus'  => true,
            'menu_icon'          => 'dashicons-admin-site'
        );
        register_post_type('uk', $uk_post_options);
    }
    add_action('init', 'cutandrun2016_post_type');



/*
 * GeoIP Detection - Guess what contry the user is in
 * https://github.com/maxmind/geoip-api-php
 */
	function get_geoip_region() {
		// This is the IP database, get country by IP
		include_once('GeoIP/geoip.inc');
		$ip = $_SERVER['REMOTE_ADDR'];

		$db = geoip_open(get_template_directory() . '/GeoIP/GeoIP-106_20150210.dat', GEOIP_STANDARD);
		$country_code = strtolower( geoip_country_code_by_addr($db, $ip) );
		geoip_close($db);

		// Include country arrays
		include('GeoIP/country-codes.php');

		// Uppercase code
		$country_code = strtoupper($country_code);

        switch (true){
            case in_array( $country_code, $europe) :
    			// User is in Europe
    			$region = 'uk';
                break;

            case in_array( $country_code, $africa) :
    			// User is in Africa
    			$region = 'uk';
                break;

            case in_array( $country_code, $asia) :
    			// User is in Asia
    			$region = 'us';
                break;

            default :
    			// User is anywhere else, assume USA
    			$region = 'us';
    			break;
        }

		return $region;
	}


/*
 * Get the users saved Region
 */
	function get_user_region(){
		// Get cookie's value
		if( isset($_COOKIE['region']) ) {
			return $_COOKIE['region'];
		} else {
			return get_geoip_region();
		}
	}

/*
 * Get the correct homepage ID for set region
 */
/*
    function get_region_home_page_id(){
        if( get_user_region() == 'us' ) {
            $home_page_id = 146;
        } else {
            $home_page_id = 558;
        }
        return $home_page_id;
    }
*/

/*
 * Get the correct homepage ID for set region
 */
/*
    function get_region_home_category_id(){
        if( get_user_region() == 'us' ) {
            $home_category_id = 10;
        } else {
            $home_category_id = 9;
        }
        return $home_category_id;
    }
*/


/*
 * Get the correct menu for set region
 */
/*
    function get_region_menu_name(){
        if( get_user_region() == 'us' ) {
            $name = 'US - Main Menu';
        } else {
            $name = 'UK - Main Menu';
        }
        return $name;
    }
*/


/*
 * Get the correct homepage ID for set region
 */
/*
    function get_region_news_category_id(){
        if( get_user_region() == 'us' ) {
            $news_category_id = 4;
        } else {
            $news_category_id = 5;
        }
        return $news_category_id;
    }
*/


/*
 * Session Tracking (disables cache on Flywheel, so region detect works).
 */
    function start_session() {
        if( !session_id() ) {
            session_start();
        }
    }
    add_action('init', 'start_session', 1);