I tried your code and it works:
I changed the wp_verify_nonce function, because that wasn’t working for me. I added an action instead of what it had. Now, for this to work, you have to create a nonce field with a code like this, of course that you can change the names if you want.
//this goes in the function that generates the metabox
wp_nonce_field( 'location_map_nonce_action', 'location_map_nonce' );
And this is the finall code of the function that save the values.
function kk_save_location_map( $post_id, $post ) {
/* Verify the nonce before proceeding. */
if ( !isset( $_POST['location_map_nonce'] ) || !wp_verify_nonce( $_POST['location_map_nonce'], 'location_map_nonce_action' ) ){
return $post_id;
}
/* Get the post type object. */
$post_type = get_post_type_object( $post->post_type );
/* Check if the current user has permission to edit the post. */
if ( !current_user_can( $post_type->cap->edit_post, $post_id ) ){
return $post_id;
}
/* Get the posted data and sanitize it for use as an HTML class. */
$new_meta_value = ( isset( $_POST['location-map'] ) ? ( $_POST['location-map'] ) : '' );
/* Get the meta key. */
$meta_key = 'location-map';
/* Get the meta value of the custom field key. */
$meta_value = esc_textarea(get_post_meta( $post_id, $meta_key, true ));
/* If a new meta value was added and there was no previous value, add it. */
if ( $new_meta_value && '' == $meta_value ){
add_post_meta( $post_id, $meta_key, $new_meta_value, true );
}
/* If the new meta value does not match the old value, update it. */
elseif ( $new_meta_value && $new_meta_value != $meta_value ){
update_post_meta( $post_id, $meta_key, $new_meta_value );
}
/* If there is no new meta value but an old value exists, delete it. */
elseif ( '' == $new_meta_value && $meta_value ){
delete_post_meta( $post_id, $meta_key, $meta_value );
}
}
add_action( 'save_post', 'kk_save_location_map', 10, 2 );