[OSM-newbies] Trust GPS or Yahoo aerial imagery?

[Chris Fleming]

Rick Collins wrote:
>> Actually, there is no way that the GPS can tell you what your 
>> accuracy is.  The various Dilution of Precision (DOP) values are 
>> simply calculations that tell you how the basic accuracy is degraded 
>> by one thing, the position of the space vehicles being used in the 
>> calculation.  There are any number of other causes of inaccuracy such 
>> as the propagation delay in the various layers of the atmosphere 
>> (typically the largest contributor to GPS error) which are not 
>> included in this calculation.  If you use a typical hand held GPSr, 
>> it will give you an "Estimate of Error" (not to be confused with any 
>> sort of real error measurement) which is based on the DOP value.  The 
>> real error can range widely more or less than this "estimate".
>>     

True, but it's all we've got to go on and in my experience  low DOP 
value traces down the same road  provide both consistent positions and 
match to other data sources at least within the kind of accuracy needed 
for our purposes....

Cheers
Chris