Hi @vana
Meta_value_num is used to sort numeric meta value. This page should give you more idea about it: https://codex.wordpress.org/Class_Reference/WP_Query#Order_.26_Orderby_Parameters.
Kindly use meta_value instead:
$the_query = new WP_Query(array(
'post_type' => 'post',
'posts_per_page' => -1,
'meta_key' => 'locatie',
'orderby' => 'meta_value',
'order' => 'DESC'
));
Hope this helps.