Fancy URL structure, conditional content, and search – using CPT, custom fields and taxonomies – SEO

After searching around, I think I can help you now.

1. Register location taxonomy to create base archive slug:

function wpso36667674_register_location_taxonomy() {
    $labels = [
        'name'          => _x('Locations', 'Taxonomy General Name', 'wpso'),
        'singular_name' => _x('Location', 'Taxonomy Singular Name', 'wpso'),
        'all_items'     => __('All Locations', 'wpso'),
    ];
    $args = [
        'labels'        => $labels,
        'public'        => true,
        'hierarchical'  => true,
        'rewrite'       => ['hierarchical' => true],
    ];
    register_taxonomy('location', 'listing', $args);
}
add_action('init', 'wpso36667674_register_location_taxonomy', 0);

We have to change the terms’ slugs which are automatically generated by WordPress to sanitized terms’ names so that the URLs’ structure look as you wished for:

function wpso36667674_filter_term_link($term_link, $term, $taxonomy) {
    $term_link = rtrim($term_link, '/');
    $pos = strrpos($term_link, '/');
    $term_link = substr($term_link, 0, $pos + 1) . sanitize_title($term->name);
    return $term_link;
}
add_filter('term_link', 'wpso36667674_filter_term_link', 0, 3);

Caution: Do not enter terms’ slugs manually when adding new terms, let WordPress generate it for us or we will not be able to query terms’ posts contents correctly. The reason is the two URLs: location/usa/ohio/cleveland and location/usa/idaho/cleveland give us the same posts because WordPress only uses cleveland as term for querying posts’ contents without caring about the parent term.

2. Register listing post type like this:

function wpso36667674_register_listing_post_type() {
    $labels = [
        'name'          => _x('Listings', 'Taxonomy General Name', 'wpso'),
        'singular_name' => _x('Listing', 'Taxonomy Singular Name', 'wpso'),
        'all_items'     => __('All Listings', 'wpse'),
    ];
    $args = [
        'labels'        => $labels,
        'public'        => true,
        'menu_icon'     => 'dashicons-location-alt',
        'menu_position' => 6,
        'supports'      => ['title', 'editor', 'thumbnail', 'custom-fields'],
        'taxonomies'    => ['location'],
        'rewrite'       => ['slug' => '%country%/%state%/%city%/%zip%'],
    ];
    register_post_type('listing', $args);
}
add_action('init', 'wpso36667674_register_listing_post_type', 0);

We’re not sure whether the listing has state|city|zip or not, so we have to use substitutes (%country%/%state%/%city%/%zip%). Then replace it with each listing meta data (From my experience with WordPress, you should store location data in each listing):

function wpso36667674_filter_post_link($post_link, $post, $leave_name = false, $sample = false) {
    $zip = get_post_meta($post->ID, 'geolocation_postcode', true);
    $city = get_post_meta($post->ID, 'geolocation_city_short', true);
    $state = get_post_meta($post->ID, 'geolocation_state_short', true);
    $country = get_post_meta($post->ID, 'geolocation_country_short', true);
    $post_link = str_replace('%zip%', $zip, $post_link);
    $post_link = str_replace('%city%', $city, $post_link);
    $post_link = str_replace('%state%', $state, $post_link);
    $post_link = str_replace('%country%', $country, $post_link);
    $post_link = preg_replace('/[^:](/{2,})/', '/', $post_link);  // Remove multiple forward slashes except http://.
    return $post_link;
}
add_filter('post_type_link', 'wpso36667674_filter_post_link', 0, 4);

Note: If your use uppercase short names, you must convert it to lowercase when modifying URLs’ structure.

3. Add rewrite rules to make our custom URLs work correctly.

// Add rewrite rules for location taxonomy.
function wpso36667674_add_location_rewrite_rules() {
    add_rewrite_rule('^location/([^/]+)/?$', 'index.php?taxonomy=location&term=$matches[1]', 'top');
    add_rewrite_rule('^location/([^/]+)/([^/]+)/?$', 'index.php?taxonomy=location&term=$matches[2]', 'top');
    add_rewrite_rule('^location/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?taxonomy=location&term=$matches[3]', 'top');
}
add_action('init', 'wpso36667674_add_location_rewrite_rules', 0);

// Add rewrite rules for listings.
function wpso36667674_add_listing_rewrite_rules() {
    add_rewrite_rule('^usa/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[1]', 'top');
    add_rewrite_rule('^usa/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[2]', 'top');
    add_rewrite_rule('^usa/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[3]', 'top');
    add_rewrite_rule('^usa/([^/]+)/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[4]', 'top');
    add_rewrite_rule('^mexico/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[1]', 'top');
    add_rewrite_rule('^mexico/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[2]', 'top');
    add_rewrite_rule('^mexico/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[3]', 'top');
    add_rewrite_rule('^mexico/([^/]+)/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[4]', 'top');
    add_rewrite_rule('^canada/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[1]', 'top');
    add_rewrite_rule('^canada/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[2]', 'top');
    add_rewrite_rule('^canada/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[3]', 'top');
    add_rewrite_rule('^canada/([^/]+)/([^/]+)/([^/]+)/([^/]+)/?$', 'index.php?post_type=listing&name=$matches[4]', 'top');    
}
add_action('init', 'wpso36667674_add_listing_rewrite_rules', 0);

4. Return back the correct terms’ slugs:

As I said, by changing usa/idaho/cleveland-idaho to usa/idaho/cleveland in permalinks, queried posts for usa/idaho/cleveland are same as usa/ohio/cleveland. So we must help WordPress know what is the correct term slug to use for querying posts’ contents:

function wpso36667674_modify_requested_url($query) {
    if ( $query->query_vars['taxonomy'] === 'location' ) {
        $slugs = array_filter( explode('/', $query->request) );
        $term = array_pop($slugs) . '-' . array_pop($slugs);
        if ( get_term_by('slug', $term, 'location') ) {
            $query->query_vars['term'] = $term;
        }
    }
}
add_action('parse_request', 'wpso36667674_modify_requested_url');

Thanks to @Jevuska for suggesting to use parse_request.

5. Create a custom template for each archive location:

Thanks to WordPress Template Hierarchy, we can do it easily.

Example:

For location/usa/ohio, the template will be taxonomy-location-ohio.php.

But remember that we must use the actual terms’ slugs which generated by WordPress, not what we modified in URLs.

Example:

If Cleveland in Ohio was added before Cleveland in Idaho, the term slug of the first is cleveland and the second will be cleveland-idaho.

Then, template for the first is taxonomy-location-cleveland.php and the second is taxonomy-location-cleveland-idaho.php.

That’s all! All code you can put directly inside functions.php file. Remember to flush the permalink settings too.