Answer:
Depending on where in the world
you are, there are a number of different answers to this
question. Generally, each manufacturer attempts to make his
GPS system as competitive as possible in the marketplace. As a
result, a good number of engineering and cost compromises are necessary
during the design of the equipment. One of these are in the area of
maps. Much of the specifics below relate to Garmin maps but the principles
apply to all consumer GPS vendor's maps.
1) Base Maps:
Base
maps do not have to be as accurate as more highly detailed maps since the maps
themselves show only the larger roads and highways and almost no city streets at
all. In an effort to keep costs low, each manufacturer purchases as
low a cost a map as possible while maintaining what they perceive as "adequate
accuracy". Generally, the maps are chosen so as to add little or no
added costs to the base price of the unit via map royalties or expensive one
time costs. As a result, you should expect that the base maps will
be off in the range of 1000+ feet (300+ meters) or more in some spots.
Generally, these base maps are ROM RESIDENT and cannot be changed or
updated in the field. Example GPS receivers with BASE MAPS include but are
not limited to: Garmin G-12Map, eMap, G-III PLUS, StreetPilot,
Lowrance GM100 and AirMap, and the Magellan 410. The newer GPSRs
such as the Garmin GPS-V, LEGEND/VISTA, SP-III, Magellan
GOLD/PLATINUM have somewhat better maps than earlier models BUT, if you
are looking for perfection, you will be quite disappointed.
2) World Maps:
World
maps are generally a step up in detail from base maps but are still reduced
detail compared with normal street level maps since the entire world is covered
on a single CDROM. The user loads the CDROM on a personal computer and
then uses the map displayed on the PC to select areas for upload to
the GPS. Generally, the World Maps are purchased, but
again, since low cost of the finished product is a significant
issue, compromises in map quality are inevitable. The World Map
quality is generally better than the base maps, BUT, you can still
expect roads to be out of position in the range of 1000+ feet (300 meters) or
more in some areas. According to Garmin, the WorldMap CDROM has not
been a big seller and so they have not updated it as of January 2002. All
of the GPS receivers noted in item #1 above can accept their vendor's WorldMap
except for Magellan which does not offer a WorldMap CDROM in their product
line.
3) MapSource Maps:
Garmin's MapSource product
line offers considerably better quality maps than are available in either
WorldMap or BaseMaps. In the USA, Garmin offers both "Roads and
Recreation" MapSource maps and "TOPOgraphical" MapSource maps. In the rest
of the world, (as of March 2000), only MapSource Roads and
Recreation maps are available. Generally, the MapSource maps are
higher quality but still less than perfect due to Garmin's desire to keep the
product sale price in the range of US$100. In the USA, these maps
are derived from US Government TIGER maps which are available royalty
free. Garmin (and many other US mapmakers) have updated and enhanced the
original Tiger Maps, and the offerings are generally accurate but with
some notable errors here and there.
In the new MapSource Maps for Europe, Garmin had to purchase maps from mapmakers in the various countries at whatever the best deal on offer. Unfortunately, map sources in OTHER THAN THE USA charge relatively high prices (and often, ROYALTIES on each unit sold) for their maps and this cost must be passed on to customers. Garmin purchased maps of the UK (and other countries) from various map vendors. These R&R maps are of good quality, but are not as detailed or accurate as the premium quality OSGB maps used in the UK MetroGuide Maps. Since substantial royalties must be paid on these maps, the cost for the UK maps is in the range of US$100 even though the UK is a much smaller land area than the US. MapSource maps will load into any of the Garmin GPS receivers noted in item #1 above among other Garmin units. MapSource maps CANNOT be loaded into any other brand of GPS receiver.
Similarly for other European areas, Garmin has purchased locally available maps for MapSource use and converted them for GPS upload. The map areas covered vary somewhat but the accuracy is generally good (but NOT perfect) and you will see some spots were the GPS places you "off the road" by several hundreds of meters.
4) MetroGuide Maps
MetroGuide Maps are Garmin's
premium map offering. These maps will ONLY load into eMap,
StreetPilot and ColorMap SP. In the USA, the high accuracy ETAK
brand maps are used (although the current MetroGuide does not have the
very latest ETAK maps). In the UK, OSGB maps are used which do
indeed provide high accuracy. Even so, you will undoubtedly find
some areas where the GPS places you "off the road" by more than the nominal 25
meters specified by the GPS specification. Some of these occurrences will
be because the GPS has a measurement error in excess of the 25 meter
specs. This is because the specification is only a 95% confidence level
specification. This means that up to 5% of the time, the error can
be greater than 25 meters. In addition, there are undoubtedly
MANY areas on even these high accuracy maps where map errors will show a
road out of its actual position by even a few hundred meters.
Similar comments apply to all of the MetroGuide Europe maps. A new Mapsource MetroGuide map for Europe is coming in 2002. This map will offer the same maps as in CityNavigator and CitySelect (for automated guidance instruments like the G-V and SP-III), but will NOT offer automatic "current position to desired destination address" guidance IN A GPS such as the G-V or SP-III. However, it will be able to generate routes on the PC which can be downloaded into Garmin GPS receivers.
5) Canadian and Mexican Maps:
Some jurisdictions
charge MUCH more for their maps than others. In Canada for instance,
Federal as well as Provincial and even Local governments closely control their
maps and charge large royalties for their use. Currently, no
vendor offers an uploadable Mexican Map because the high costs relative to
sales potential make the final product too expensive for consumer level
equipment. Maybe all this will change if enough of "you
folks" protest that this situation is causing you to go without maps in your
GPS. Garmin offers an uploadable Canadian map system for their
equipment only.
6) Australian Maps:
The GME representative in
Australia has stated that high detailed maps of Australia (apparently including
automated guidance capability) will be available in early 2002. I have not
seen these maps, but they should be welcome as they will be the first such
maps in the Asia Pacific sphere.