[Plugin: Basic Google Maps Placemarks] using placemarks in my footer widget?

So, you’re putting the shortcode inside a text widget? I think you’d need to do two things:

1) Add a line of code to your theme’s functions.php file so that shortcodes in widgets will be processed — https://digwp.com/2010/03/shortcodes-in-widgets/

2) Add this code to your theme’s functions.php file:

function your_theme_name_bgmp_shortcode_called( $mapShortcodeCalled )
{
    return true;
}
add_filter( 'bgmp_mapShortcodeCalled', 'your_theme_name_bgmp_shortcode_called' );

I followed the instructions above and pasted the following into wp-includes/functions.php exactly like this:

add_filter('widget_text', 'do_shortcode');
function your_theme_name_bgmp_shortcode_called( $mapShortcodeCalled )
{
    return true;
}
add_filter( 'bgmp_mapShortcodeCalled', 'your_theme_name_bgmp_shortcode_called' );

It did not allow the text widget containing [bgmp-map] to work.

Am I taking your instructions too literally? Please be clearer so I can understand.