Dashboard widget location

I want to create aplugin to add a widget to the Admin Dashboard.

It works fine except I cannot work out from the core files how to make the new widget occupy the side rather than the main column when it is first installed.
$location = ‘side’ seems to be the code, but where to place it.
I have:

<?php
function thistheme_admin_dashboard_widget_a() { ?>
	Content A
<?php } 

function thistheme_admin_add_dashboard_widget_a() {

	wp_add_dashboard_widget('thistheme_admin_dashboard_widget_a', 'Widget A', 'thistheme_admin_dashboard_widget_a');
}
add_action('wp_dashboard_setup', 'thistheme_admin_add_dashboard_widget_a' );

?>