YOu mean filled at registration?
First you'd have to add the location field to the registration form (not there by default). For that, you could add in a plugin at
register_form_start with something like...
PHP Code:
$human_verify .= '<input name="location" type="text" />';
(You'd definitely want to tweak the HTML to look better.)
Next you'd want to make a plugin on
register_addmember_process to check and add that info. Something like:
PHP Code:
$location = $vbulletin->input->clean_gpc('r', 'location', TYPE_STR);
if (!$location) {standard_error('HERPADERP, YOU FORGOT THE DARN LOCATION!',false);
$location_array = array('field2' => $location);
$userdata->set_userfields($location_array);
That -should- do you... but tbh, someone's probably already created a plugin for something like that. If not, just twaek that code, test it out, see if it works for you.