Something is amiss with Google’s map data for St Austell. It has never been as good as Truro's but it used to be that you could at least make out house roofs and streets. Compare the two images taken from Google Maps, they are both at the highest resolution for the respective areas:
You can see this for yourself here:
Repeat - Thats the same resolution in the St Austell and Truro Map images.
See for yourself at http://maps.google.co.uk/maps/