Tuesday, May 24, 2005 at 22:22
The inaccuracy is the map, not the typical 6 metre inaccuracy of the GPS. a road width is only 6 metres and your Etrex will only show a 5 metre zoom max. The basemap is not based on the datums the GPS uses to position itself, it is said the map is older than GPS and my belief is that because the map is accurate sometimes but mostly not the map has not been ported into the Garmin using the same datum. It would be like overlaying Streetsmart and a UBD street directory that are scaled differently and inherent printing errors. The fact that stirling highway in
Perth runs along in the Swan river rather on its banks is clear to me the map is shifted too far to the left and south, however other areas it is spot on or too far the other way. That's why you get the road shifting from one side to the next on your GPS by several hundred metres in some cases.
Metroguide and City Navigator uses a database (known as a dataset) from Whereis, which is a division of Sensis and is owned by Telstra. If you look at your street directory you may find it has the Whereis or Sensis logo on it. The dataset within major
population areas are extremley accurate, down to around a metre or better, whilst country towns and roads are based aerial photographs ( a few metres) or in some cases satellite imagery (10 metres). Thus on the outback roads you may find the road shift as far away as 10 metres to either side. Much of this country stuff is from MapInfo. There are bound to be some aerrors, and at the Whereis web site you can put in a form to let them know where the serious errors occured that you had found on your trips.
On the Whereis web site you will see they brag about who uses their datasets.
I hope this has enlightened those who were confused rather than confusing them more :)
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