Automatic Address to Address Routing GPS Automobile Navigators
What to expect from the currently available equipment
Revised 1/28/2004

By Joe Mehaffey

The latest innovation in GPS hardware is the ability of hand-held/portable units to automatically compute quickest and/or shortest routes to a destination.  The currently available handheld and portable GPS Automobile Navigation systems are indeed impressive, in that they can replace OEM  installed units costing from $2,000 to $3,000.  However,  many people expect more than these units can deliver because of current technology limitations.  This article covers the most important features, so you will have a better idea of what to expect if you buy one of these GPS Automobile Navigators.  You can find product reviews of some of the more popular units such as the Garmin StreetPilot III,  VDO Dayton,  Alpine and others HERE.  (Note:  The following specifics relate to USA users,  but most suggestions apply universally.)

Routing:  Generally speaking,  the program generated routes by modern GPS equipped automatic address to address routers are pretty good.  If you think the current crop of autorouter programs will/might/or ought to be as good as or better than the one that a person knowledgeable about the region would pick,  FORGET IT!   If you know of a route that can save you 5 minutes on a half hour trip and you think the route designers are "stupid" for not having their program do better.  THINK AGAIN!  Designing a program to sort from thousands of route possibilities and pick a "pretty good" route using the extremely limited computing power in today's autorouting GPS units is little short of awesome for folks who have knowledge of how this is done.

The best models do, more often than not, produce a high quality route that will get you from A to B in a reasonable time.   The latest models with NavTech maps sometimes will surprise a person with a better route than the one normally used.  If you find a map error in a NavTech Map (used by Garmin, Magellan and many others is SOME of their equipment) go to this DRIVER FEEDBACK website and enter the information about the map error you have found.  It will help ALL of us!  

Most models automatically recalculate a new route for you whenever your route deviates from its expected route.  This does allow you to use your own judgment when emergency situations arise and you still have the detailed map information of the GPS  to route you to your final destination by some alternative route -automatically computed without any need for an input by the user.  A few models (Such as StreetPilot III, SP2610/2650 among others) can detour you around a road stoppage upon your request.  (See product reviews.)

However,  your GPS cannot know about your favorite route,  your favorite kind of road scenery,  or your preference to take a route home so as to  stop for a beer at Sam's Bar on the way.  In years to come,  expect to see GPS Navigators  (Such as VDO Dayton today) tied in by radio to traffic information so as to automatically route you around traffic difficulties.  But such systems TODAY are in their infancy and VERY few cities provide the necessary radio data stream to make such a system work..

Data Input and Programmability:  Most units provide a reasonably easy means to input addresses and route specifics.  Most use some sort of four position rocker key to select letters/numbers for an address or other route details.  Many use a "matrix" style down/over/enter to pick a letter.  The latest units such as the Magellan RoadMate and the Garmin StreetPilot 2610/2650 use a touch screen for input of most data.  Most units try and assist the user by anticipating what the next letter(s) might be so you can just "finish" when enough of the name appears on the screen.  This is not something you need to be doing as you drive along,  but a stop for a 30 to 60 second period will usually get a new address into a machine after you have done it a few times.  The only units we have used with a full keyboard have been those which run on some form of general purpose computer.

GPS Receiver: The receiver provides the means to locate your position in longitude, latitude and perhaps altitude.  It is typically accurate to about 10 or 20 feet assuming you use an antenna on your car with a good view of the sky all around your car.  If you let your antenna look out the front windshield only or the rear window only,  measurement accuracy will be worse and you can expect that at least occasionally you will lose satellite lock,  BUT  most of the time your system will still work just fine.

WAAS:  Car navigators do not have and do not need WAAS or DGPS accuracy augmentation.  Instead,  the icon is locked to the road you are on and knowing your position on the road  to an accuracy of +/- 20 feet is always (IMHO) good enough.

Maps:  The maps required for a GPS automatic navigator which can design you a route from address A to address B are highly specialized.  In addition to the need for highly accurate maps,  the map database must contain a large amount of data about highway and roads.  This road information includes average travel speed classifications, one way streets,  names and road numbers of all streets,  expressway ramp details, and dozens of other programming details.

One of the main disappointments of some people is that the maps are NOT PERFECTLY ACCURATE or they find their favorite street in a subdivision is missing.   Forget it.  None of the currently available maps are perfectly accurate.  And they do not have to be perfectly accurate for the user to receive quite satisfactory results.  For instance,  roads and highways are being built,  moved,  and renamed and renumbered all the time.  Many municipalities are lax in getting their changed map data to the proper agencies and are in arrears for YEARS.   Generally speaking,  maps appear to be from 2 to 4 (or even more) years old.  Some roads (even Interstate Highways) can be out of position by hundreds of feet in spots.  (So many roads,  so few map makers.)  As a result,  you cannot pick up a single printed or electronic map that is completely accurate.  Some ARE better than others.  NavTech  maps are among the best.  BUT!  Don't expect perfection!  You won't get it.

NOTE:  The above comments apply to the REALLY GOOD quality maps by NavTech and a few others as used in Car Navigation systems.   The "not so good" quality maps (such as Garmin R&R,  Lowrance Streets, and Magellan MapSend Streets,  the WorldMap offerings and basemaps in handheld units)  can have much larger errors.  I have seen roads displaced by almost half a mile in a few spots.  Sometimes the shoreline on basemaps is displaced so you seem to be driving in the water.  Forget it!  Things are improving every day,  but perfection is quite a ways off.

Points of Interest: Large arrays of information are provided to identify,  sort,  and locate such entities as restaurants,  gas stations,  hospitals,  garages,  parks,  and dozens of other specialized variants.  Most systems have many tens of thousands to MILLIONS of these POI.  Expect that some small percentage of the listings will be out of position, missing entirely,  or have the business name changed from what is listed or  phone number wrong.  It is easy to understand that with the fluid nature of business locations,  this will always be a problem.

Portability:  Many of the older and more expensive units are designed to be permanently installed in your vehicle.  A few such as the Garmin StreetPilot 2610/2650, Magellan RoadMate 500/700,  Garmin GPS-V are designed to be  easily moved from car to car.  For most purposes,  portability is a plus unless you require some specific feature(s) provided in the permanently mounted units.

Adjunct Positioning: Some units have an acoustical gyroscope,  compass, or some form of "dead reckoning" means to provide interim guidance for momentary situations where GPS signals are blocked.  The simpler approach of doing without adjunct positioning input works well except in highly built up areas such as center New York City, City of London, and etc.  The units with some form of adjunct positioning typically cost over US$2000 (except for the Garmin SP2650 at about $1200) and are permanently installed in a car.  If you were going to use a unit mostly in the center of New York City or London,  (and needed guidance there) you would want a unit with some form of adjunct positioning.   If "city canyon" driving is infrequent,  it's doubtful the added expense would be justified.

Picking the unit best for you:  We suggest you first read the information HERE.  Then read our product reviews of the Magellan RoadMate 500/700,  Garmin StreetPilot 2610/2650StreetPilot III, iQue 3600,  VDO Dayton, Alpine, Garmin G-V and others.  Search other websites for references on GPS Automobile Navigation Systems.  Get a demonstration.  Ask your friends and users on the GPS NewsGroup (HERE) for their opinions.  Then you might try THESE discount internet dealers for your best deal.  You will be wise to do your research FIRST and buy later.  These units are not all the same, and they cost a good bit of money.  Everyone has special wants and needs and checking the specifications before you buy is the way to get what you want.  MAKE SURE you can get good maps for your areas of interest BEFORE you buy any unit.

Problems YOU will see with current Car Navigation Systems.

Suggestion for new owners of GPS Car Navigation Systems:  These units are GOOD,  but they are NOT perfect.   Don't expect that all routes generated will be as high quality as you would design yourself.  (If the Car Navigator does propose a route not to your liking,  just drive the route you want and the GPS Navigator will recalculate and catch up.)  Expect that not all address numbers will be included in the data base.  Expect that some small percentage of streets will be missing, slightly out of position, or mislabeled.  Expect that many (if not all) systems will not have as much detail as you would like in rural areas.  (NavTech delivered in 2002, maps for GPS Navigation which are of good to excellent quality and include full USA coverage.  In 2004 the third major update will be delivered to Garmin/Magellan, et al.  All major car navigator vendors use NavTech maps as at least one of their offerings.)  If you can accept these occasional limitations,  you will get a lot of utility out of your equipment.   If such things tend to frustrate you and you expect perfection at this stage of the technology,  wait ten years.  But in the meanwhile,  you will be missing out on a great new tool for your automobile travel.

Other Details:
1) The maps available today (regardless of price,  vendor or area) are not perfect and will have error in road positions,  POI positions,  and some roads will be missing.
2) Routing will generally be VERY good,  BUT,  there will be problems with some routes generated by ANY of the presently available car navigators.
3) If you try and do MANUAL routing,  (uniquely available in Garmin's SP-III and G-V),  it will work modestly well,  but these units were designed for AUTOMATIC routing and you should expect that manual routing will not be as easy to use or as predictable as in other units.
4) All vendors (that we know of) now provide full USA map coverage in car navigators.  Coverage in Canada is limited at best,  Mexico and South American coverage is just the basic "World Map" coverage with no routing.  Western Europe is covered pretty well.  NavTech Maps are the best available,  and the LATEST NavTech maps provide full USA coverage to residential street level.  The amount of map coverage and the price for additional covered areas (such as Europe, Australia, South Africa) varies from vendor to vendor.   Coverage in the Europe varies.  Some areas are full coverage,  others spotty.

While the Garmin units are <often> much more useful overall because of their wide array of  map capabilities,  problems can arise when you MIX the various map data in Garmin units.  If you automatically create the route on the PC with City Select and transfer it to the unit...and you have all those CS/CN detailed maps the route uses loaded into the will work fine.  It all matches and the unit has no problem with it.  When you do not have all the relevant CS/CN detail loaded and transfer the other words, the route runs off of the loaded CS coverage and into basemap or other different coverage (i.e., MetroGuide) has to recalculate because it is routing across different map data.  It has to make the route work...and with the differences in the data, it cannot do that without recalculating.  Even if you have CS/CN and MG detail loaded...and even if the loaded maps line up next to one another or overlap...the unit will have to make that jump between the different maps...and it recalculates.

We no longer recommend manual routing for car navigation though it is available in some units.  Use of manual routing is tedious and the GPS units which offer this typically operate with lots of recalculations because of waypoint errors or map errors relative to the waypoint position.  In our opinion, manual routes are no longer needed with the improvements in routing.  Many Garmin units do offer VIAs so you can direct your Car Navigator to take you along a special route.

Details and Solutions:
1)  "Less than perfect" routing results can happen with limited memory  and CPU power when the route is mixed between basemap and detailed maps. The problem is that a route is found on the basemap well before any paths trying to find their way along detailed roads find a complete route. Eventually, the algorithm gives up looking for routes and just takes the best one it has so far, (perhaps) a basemap route.  The latest Magellan and Garmin Car Navigators with high speed processors and lots of memory dramatically improved this situation,  but you may still occasionally see quirky behavior.

2)  The best solution is for the user to load detailed maps for the whole way, especially when it's a route that goes in and out of detailed coverage areas. The basemap routing works best when the detailed coverage areas are completely separate, like going from NY to LA with only details at the ends"

3) Joe and Jack recommend that Garmin users of automatic routing units in the USA use Garmin CityNavigator 5 or City Select 5 and not mix maps between the two map packages.  This appears to be more problem free than mixing CN/CS with the basemap or with MetroGuide USA and the basemaps.