Try the following regular expression:
/http:\/\/maps.google.com\/maps\?q[^"]+(?=")/
But the page may contain similar URLs outside the HTML structure you've presented, then it's better to use a more complicated regexp:
/(?<=<tr><td><a href=")http:\/\/maps.google.com\/maps\?q[^"]+(?=">map<\/a><\/td><\/tr>)/