Why is my G-III Map Accuracy not perfect?
I asked Garmin Engineering to comment on,  "How accurate should a 
customer  expect his map to be in the new G3?" and "Are the  maps 
in the G3 International Version as accurate as those in the USA?"

Here is the response from Garmin Engineering:  (10/23/97)
We  understand that customer expectations are quite high for  map 
accuracy on the GPS-III,  perhaps much higher than what the  unit 
was designed to be capable of.

Map data in the US is quite complete and fairly accurate,  though 
that  is  not  to  say there may not  be  some  minor  errors  or 
ommissions in the included data.
Map  data on the GPS III for areas outside the USA  unfortunately 
will  almost  always be of less detail and accuracy than  in  the 
USA.   This is because good quality electronic map data  for  the 
USA  and  to  a lesser extent for Canada and  Mexico  is  readily 
available  free or very low cost. 
Virtually  all other countries around the world charge  for  this 
type  of  data,  if  you can get it  at  all.  We  had  difficult 
decisions  to  make  as far as what data  to  purchase,  what  to 
digitize  ourselves, and what to leave out.   We did the best  we 
could given the cost,  and potential customer base to pay for our 
For  the International mapping data we had to rely on  government 
publications  and  mapping  which were at  times  dated  and  may 
contain inaccuracies and ommissions.   Again, we did the best  we 
could given the cost constraints of the unit.
Clearly,  if the International customer(s) could  convince  their 
governmental authorities to make available good quality digitized 
mapping data for free or a reasonable cost, we would be more than 
happy to incorporate the data in our base-map.
Due to memory constraints, the data is only stored in the unit to 
a specific level of detail.  When the map is zoomed in beyond the 
stored  accuracy  of  the data,  the  data  is  interpolated  for 
display  purposes, and OVERZOOM appears on the map to  alert  the 
user  that the map is  displaying interpolated data with  reduced 
accuracy.    Naturally,   if  you examine  the  position  of  map 
features  displayed with interpolated data,  you will often  find 
roads  and  other features displaced from  their  real  location.  
This often happens when straight lines replace curves.
The finest zoom scale that we show without indicating OVERZOOM is 
3 nautical miles, which represents  approximately 250  meters per
pixel.  If  a customer   observes  an  inaccuracy of say  400-500  
meters,  this represents 2 pixels of error on the minimum useable 
scale,  which  should  still  show  you  on the road in question,  
UNLESS the  unit is overzoomed and using interpolated data.
NOTE: This means that at MAP SCALES BELOW 3 MILES you may observe
errors GREATER than 500 meters due to interpolation of map data.

A few map sections,  particularly in the International  Versions, 
have  offsets of several hundred meters.  This was a function  of 
the  accuracy  of  the  source map data.   Again,   due  to  cost 
constraints  on  a product of this type,  it is not  possible  to 
verify the accuracy of individual maps furnished to us.  As  maps 
themselves improve,  they will be incorporated into our products.
     Best Regards,
     Garmin Engineering
     Olathe,  Ks. USA

Note from Joe:
I just got back from a 1500 mile trip in the Eastern USA with the 
G3.      I  found  the maps uniformly accurate with  just  a  few 
exceptions.   Considering  the VERY limited map memory  used,   I 
think most will agree the USA map accuracy is very good.  When  I 
was  touring Europe earlier this year with MicroSoft AutoRoute  5 
(CDROM  maps),  I noted errors in Europe and the UK in excess  of 
1000  meters  MANY  times.  MicroSoft's comment  on  my  accuracy 
findings was much like those of Garmin above.  Apparently the USA 
is  very  fortunate to have the USGS and related  agencies  which 
have  done  an excellent map making and digitizing  job  and  put 
their  work  into the PUBLIC DOMAIN where all of us can  use  and 
enjoy these high quality maps.

I  hope our overseas friends will get on the telephone  to  their 
government  mapmakers  and  get all agitated about  the  lack  of 
inexpensive  high accuracy digital maps.  This would help all  of 
us in the long run.

Joe Mehaffey