WP Geo with hidden posts

I am using WP Geo 3.3.8 on my page to generate maps from posts containing the location of my boat.

I have a positions page with the following code on it that produces a map showing historical positions but only shows the content of the latest post( the post title contains the date and time it was sent).

Received on&nbsp;<?php query_posts('category_name=Position&showposts=1'); ?>
<?php while (have_posts()) : the_post(); ?>
<a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
<?php endwhile; ?>
[wpgeo_mashup numberposts="50"]

I do not want these posts to appear in my normal blog page so have tried adding code similar to this

function exclude_category($query) {
if ( $query->is_home() ) {
$query->set('cat', '-8');
}
return $query;
}
add_filter('pre_get_posts', 'exclude_category');

to funtcions.php as described in many places on the net.

When I do this my position map no longer contains my positions although the Received on xxxxxxxx part shows correctly the title of the last post.

Any ideas?

Chris

https://wordpress.org/plugins/wp-geo/