By default, the “Marker Categories” taxonomy (oum-type) used in Open User Map is non-hierarchical — this means it behaves like tags, showing up as a text input field in the editor where you can type and separate items with commas.

However, in some cases, it’s more user-friendly to show a checkbox list, like the standard WordPress Categories interface. This guide shows you how to force WordPress to display the oum-type taxonomy as a checkbox list, without changing the underlying structure of your taxonomy or modifying the plugin.

🧩 How to implement

1. Open your active theme’s functions.php file
   (or better: use a code snippets plugin to keep changes safe and theme-independent).
   
2. Add the following code:

function oum_force_checkbox_ui_for_oum_type_taxonomy() {
    global $wp_taxonomies;

    if (taxonomy_exists('oum-type')) {
        $wp_taxonomies['oum-type']->hierarchical = true;
    }
}
add_action('init', 'oum_force_checkbox_ui_for_oum_type_taxonomy');

🔁 What does this do?

This snippet overrides the UI behavior of the oum-type taxonomy by telling WordPress to treat it like a hierarchical taxonomy — just for display purposes.

• Your data stays the same.
• The taxonomy still behaves like a tag system under the hood (flat, non-nested).
• In the post editor, you’ll now see a list of checkboxes instead of a freeform input.