WordPress at a glance
filter is not described

wp_nav_locations_listed_per_menu filter-hook . WP 3.6.0

Filters the number of locations listed per menu in the drop-down select.

Usage

add_filter( 'wp_nav_locations_listed_per_menu', 'filter_function_name_9779' );
function filter_function_name_9779( $locations ){
	// filter...

	return $locations;
}
$locations(int)
Number of menu locations to list.
Default: 3

Where the hook is called

In file: /wp-admin/nav-menus.php
wp_nav_locations_listed_per_menu
wp-admin/nav-menus.php 705
$assigned_locations = array_slice( $locations_assigned_to_this_menu, 0, absint( apply_filters( 'wp_nav_locations_listed_per_menu', 3 ) ) );

Where the hook is used (in WP core)

Does not used.