If you want to print a numeric value which is a variable plus something ($location + 10), you have to do this :
<?
echo "<p align=\"left\"><font face=\"Verdana\" size=\"2\">";
echo "<a href=\"http://www.majesticarts.co.uk/exordium/navengine.php?location=" . ($location + 10) . "\">North</a>";
echo "- $areadata[19]</font><p align=\"left\"></p>";
?>
If you don't do that, you will have something like (if $location = 155, example...) : $location=155+10. Also, as I did, remove the $ after the ?. If you don't, it will not print the word "location", but the content of $location...