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What is a "Mapping" GPS Receiver?

by Larry Klementowski

First, this article assumes you have at least a passing knowledge of what the Global Positioning System (GPS)  is, and what a GPS receiver (GPSr) can do. You don't need to know how it works, only what it can do--which, in a nutshell, is to tell you where you are on or above the earth's surface, with the help of the GPS satellites in earth orbit. I'll be talking about the handheld GPS receivers generally used for recreational purposes such as hiking, geocaching, biking, car navigation, bench mark hunting, and so forth.
So, what is a "mapping" GPSr, anyway? In the most simple terms, it is a GPSr that shows your present position superimposed on a map displayed by the unit. This can be very handy, but there is a huge variety of different ways the map can be presented, and in the quality or content of the map.
Early handheld GPSr units (we'll just say GPSr from now on, but we mean the recreational handheld units) only presented data in text or numeric format. In other words, it gave your latitude, longitude, altitude, and other data in numbers, and you had to take it from there. Surprisingly, there are still quite a few GPSr models being made and sold that do just that, and little more. They may be a bit more accurate and use less battery juice than earlier units (say, one from 1990), but they still do basically the same thing.
Then, not too many years ago, someone had the great idea to mark your current position on a simple map stored in the GPSr, and mapping GPS receivers were born!
From there, mapping GPSr units were improved in fairly small steps to the current state of development, which is in many ways quite remarkable. You can even buy one now that downloads real-time weather radar maps via the XM Satellite Radio system! When I heard about that capability, it really hit me as a great idea! At present, only the Bushnell ONIX400 can do that (to my knowledge). But back to more common units for now. We'll refer to the table below in the remaining part of this article.
Disclaimer: The "generations" below are my opinion only, and are not meant to be set in concrete, or to represent any sort of industry standard. Don't expect your GPSr dealer to know what you are talking about when you ask for a third-generation mapping GPS receiver!

No mapping capability
Garmin eTrex (basic yellow model)
Magellan GPS 2000
Rudimentary mapping; basemap only
Garmin eTrexVenture
Uploadable street and topographic maps
Magellan Meridian and eXplorist
Garmin GPSMAP 60Cx
Uploadable street maps; very detailed topographic or USGS raster topographic maps or aerial photos
Delorme PN-20
Bushnell ONIX200CR
Generation 3 plus real-time XM satellite-linked NEXRAD weather radar
Bushnell ONIX400

Mapping GPSr Generations

I think we all know what a street map is. It shows streets, roads, highways, and similar transportation corridors. It might even show bike paths, railroads, and some other basic information. But what is a topographic (topo) map? In short, a topo map shows the shape and elevation of terrain features by the use of elevation contour lines (isolines). A contour line is simply a line on a map that is drawn at a constant height. The height or elevation is normally elevation above a certain given starting elevation, such as mean sea level. Contour lines allow terrain to be visualized on a flat surface. Historically that surface was paper, but today, it’s often a computer display. Why is this useful? If you're hiking or biking, it sure is nice to know what's in front of you: a nice easy uphill, a steep downhill, or a cliff!
Here is a simple topo map, representative of the type available on early Generation 2 GPSr units. The elevation contours are widely spaced, and not a lot of additional information is present. Yet I was happy to have similar topo maps from Magellan Mapsend Topo  on my Magellan  Meridian Platinum for years--even though it only had a black-and-white display! Garmin has similar capabilities available on its GPSMAP series and some other models. These simple topo maps are certainly useful, but now, better quality topo maps are available on GPS receivers.
The next topo map example is from Delorme Topo USA 6.0, and represents what is likely the state of the art in current topographic maps--what I call a Generation 3 mapping GPS receiver. There is obviously much more data present, both in terms of contour lines and other data. An important word above is current. These maps are maintained by the manufacturer, and updates are available periodically. One problem with the USGS topo maps discussed below is that they are not maintained, so the data on them can be 20 or even 30 years old. Not a good thing if you are looking for a street name. On the other hand, terrain rarely changes much in many areas of interest to wilderness hikers, geocachers, bench mark hunters, etc.

Currently, topo maps of this quality are available on Delorme and Bushnell  GPSr units. Other GPSr manufacturers are sure to follow soon. Magellan's recently announced Triton series will probably fit into my table as Generation 3 units.

Shown next is a topo map taken from a publicly available U.S. Geologic Survey (USGS) 7.5-minute topographic map, which gets its name because it covers 7.5 minutes of latitude and 7.5 minutes of longitude. The 7.5-minute maps are often referred to as a "quadrangles"or simply "quads," although quads of other resolutions also exist. This electronic (scanned for use on computers) version of a USGS topo map is known as a digital raster graphic (DRG).
7.5-minute quads have more details of contours than on the rudimentary topo map shown earlier, and lots of other good information. This would be another example of a Generation 3 mapping GPSr. Having this map available on your GPSr--as I do on my Delorme Earthmate PN-20--is a very nice feeling.
Is it overkill? Maybe. It really depends on what you're doing, doesn't it?

Do you see the "BM 747" near the top left of the USGS topo map? Serious bench mark hunters will recognize that as a USGS bench mark, and find it handy to have on their GPS receivers. It would not be present on an older unit. As an avid bench mark hunter, I find this built-in bench mark information very useful! By the way, the area pictured in the above topo maps is in large part Chino Hills State Park in Southern California. I'm quite familiar with the area--with or without topo maps--and I was quite impressed the first time I went there with a handheld GPSr that had USGS topo maps on it. As they say, it blew my socks off! (Not good when you are hiking! :-) ).

In addition to topo maps, Generation 3 GPSr units can display aerial pictures, similar to what you might see on Google Earth. Depending on the area you want to see, and what model of GPSr you could afford with your budget, the aerial maps may either be in black-and-white or color. The example at right is taken from a public domain USGS digital orthophoto quarter quadrangle (DOQQ). At present, to get these or similar aerial pictures, you need to purchase them from your GPSr manufacturer--and they tend to get somewhat pricey. Delorme and Bushnell give you some credit in a "starter" account to get you going on aerial photos.



The last entry in my generation table at the beginning of this article is Generation 3+ . At this time, it's represented only by the Bushnell ONIX400. This unit not only receives signals from the GPS satellites like other GPSr receivers, it also receives signals from the XM Satellite Radio system--the same system you might have in your car. What's the big deal? Well, not only can you listen to the radio, but you can also download real-time NEXRAD weather radar maps for your current location The GPSr superimposes the weather map over your current map or aerial photo, along with your present position and other waypoints. Imagine being out on the Pacific Crest Trail or the Appalachian Trail for several days, and wondering whether you should try going over that pass ahead with those threatening clouds looming. With this unit, you would be able to see just how severe the thunderstorm activity is, with maps only minutes old. Amazing technology! Note: Because of XM's satellite coverage, this capability is currently available only in the U.S. and near off-shore areas.

So, what type of unit do you need? How much mapping data? Only you can answer those questions. Remember that in addition to the map and your present position, all mapping GPSr units will also include symbols (of various designs and qualities) that represent stored waypoints such as geocaches, bench marks, and trailheads. Also, a GPSr can show plotted routes (where you want to go), and recorded track data (where you have been) on the map. To borrow a word from my Air Force days, the "situational awareness" of a Generation 3 or 3+ GPSr is fantastic!

There are many resources available on the Internet and elsewhere that will give you the specifications of any new GPSr you are thinking about buying. Be sure to ask (or read) what kind of maps (streets or topos) can be uploaded into the GPSr, where they come from (what software package), and whether that software comes with the unit (some does, some costs extra). If possible, look at some of the maps.
Memory space available on the unit is important, too. Those detailed topo maps can eat up memory in big chunks of megabytes, so note whether the unit has user accessible memory cards (such as an SD card slot). Also, test how long it takes to display a new map. The update speed of the screen depends on what kind of map you're viewing, and what kind of memory the GPSr uses.. Moving all that data around inside the GPSr can take several seconds, but if high-quality maps are important to your geocaching or bench mark hunting, you'll probably find it worth the wait.

The Resources section of Caching Now has links to other websites that may help you decide what mapping capabilities you need in a GPS receiver. The links in this article might also prove interesting. So the next time you fire up your GPSr to go geocaching or bench mark hunting, maybe you can do it with the help of some great maps! Enjoy!


Larry Klementowski (aka Klemmer or Klem) is an ex-USAF pilot, now part owner of Sekai Electronics, and is involved in various high technology video related projects, including some specialized GPS receivers for aircraft applications. He can often be found out geocaching (590 found, 46 placed) or bench mark hunting (278 found), usually while hiking or mountain biking.  Larry and his wife Julie are also dedicated Disney fans, often walking at Disneyland to check on their Downtown Disney and DCA virtual geocaches, and Berntsen's Disney bench marks!

Originally published on September 15, 2007.



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