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I am an infrequent hiker but love to hike. Last year, I lost the trail in the Whites (despite perfectly fine blazes, I was sorry to see...) for about an hour. I always hike with a map & compass but thought I might want a GPS to let me know if I am actually where I think I am on the topo. So, I am looking at a couple of Garmin units and have not been able to find a salesperson at a couple of stores who actually uses one! My question is pretty basic - the topo maps that can load onto a GPS such as National Geo topo do not have many trails marked as best I can tell. How does one match up a digital topo map in a GPS unit with a trail outlined and mapped in, say, the White Mountain Guide's maps, so that the unit will actually know where I am in relation to a trail? If you know of a good reference guide that may help me answer this...or if you can answer this...I would apreciate it very much. Thanks. Dom

a gps gives you a point on the earths surface. your trail is a series of points on the earths surface. when you start out on a trail, set the gps track log on. as you move, the gps will keep a track log of your position. set it for fixed distance say 50ft. when you are lost, look at the breadcrumbs on the gps log and multiple by 50ft to get distance on the trail or to see where you are on the trail, look at the breadcrumb track log shape and compare it to your guidebook. the two should be identical.
anyway, garmin contour maps along with hiking trails are available so if you had a 60csx with the correct garmin maps loaded you could ditch your paper maps. not that i recommend doing that since batteries can fail so a paper+compass as a last ditch backup is always useful.

Dom:

Based on what you have described, this is my recommendation.

The GPS topo maps available for US are not that detailed, except for national parks. I would assume your paper topo maps would have more details. There are many forest service paper maps that will show small trails and logging roads, and most likely a GPS topo map will not even have them identified. So, if you often hike in areas such as these, I would recommend an inexpensive GPS unit.

Any basic GPS, including units in the $50-$100 range, will do you nicely, even a 10 year old unit. They do not display maps and are monochrome, but they will show you where you have been via breadcrumbs, will keep many waypoints, and most important, it will give you your exact location in latlons. All of your paper topo maps should have latlons in the margins. So you can just read the latlon from the GPS, and find your location on the paper maps. This is very accurate, quick, and very inexpensive.

I have been using a GPS for sailing from way back in 1994, a Garmin-45. Before that, I used a loran. In fact, that is the way most people have been navigating the seas for many many years. My Garmin-45 unit has taken me from Seattle to Alaska and back via the inside passage, and out in the wide open Pacific Ocean. I also have a Garmin 76CSx, and I do have the US streets using Garmin's City Navigator mapping and routing software. When I am driving in unfamiliar areas, I do use it for street routing. But when I am on the water, I do not use any kind of marine map on the GPS. I use the good old latlon, and then look up my current location on the paper marine charts. Recently, I have installed a navigation charting system (non-Garmin) that integrates with a GPS and radar display, but I still use paper charts, and I draw and make notation on paper charts.

Paper marine charts of almost every little chunk of water on this planet are available from many agencies, in almost every country. But they are not always available in GPS form. The same would apply to your topo maps. That is why I am recommending using GPS for the latlon, and use the paper topo maps for your trails.

If you want to spend more money, the 60CSx and 76CSx are excellent units. Even with these units, you may not be able to get the detailled GPS topo maps for the area you are hiking in. You can go to Garmin's website and view the actual topo maps online to make sure.

One additional piece of information that may be of interest to you. Your GPS latlon and your paper topo map may not be identical. In fact, they may be very different from each other. It all depends on how accurate your maps are. When sailors go to many parts of this planet, their GPS latlon may sometimes be many km away from their charts. It all depends on how the original map/chart maker created the maps. Some mariner charts were drawn back in the early 1900s, and some go back into the late 1800s, and some of them are still in use today. And, if they updated them recently, they may not have used a GPS to create them, so some of the maps are not that identical to a GPS. This same situation may apply to topo charts too.

Thanks to both of you for your thoughtful comments. I have a better sense of where GPS might fit and what the limitations of it as well as the maps are. It seems like choosing a detailled map source for accurate topos with trail info is as much, if not more important than the unit itself.

As a first step, I purchased "Be Expert with Map and Compass"! Thanks again. Dom

Dom: You are very welcome.

You may want to look into an inexpensive GPS, and Garmin does have a number of units. As I have said earlier, these inexpensive $50-$100 units will give you your current position in latlon. If you are only using your paper topo maps, you may not know exactly where you are in relationship to points on the paper map. At least if you also have a GPS, you can look it up on the paper map, and you will never be lost.

Have fun hiking.

I must Say That was A Very Informative Reply Thanks
From another onlooker..

Dom, I think the best solution for your purpose would be to purchase a program like National Geographic Topo for your state/region. This map series is a 1:24,000 scale and allows you to browse the entire map on your PC. It also has tools that allow you to plot routes on the topo map which you can convert to GPS routes and upload to your unit. This way you have your entire trail uploaded to your GPSr, along with whatever extra waypoints and POIs you may want available on your hike. You can also use the topo software to print out a detailed topo map to take with you on your hike.

It's important to understand that this National Geographic Topo software will NOT work on your GPSr itself. GPS units use proprietary software from their manufacturers to display the maps. Also, aside from national parks, the best scale you can get currently is 1:100,000. This is why it's so desirable to use a 1:24,000 topo map to plot your hikes in advance.

Read this article for more on the differences between GPSr maps and PC maps: http://www.handheldgpsinformation.com/gps-maps/gps-maps---raster-or-vector.html

Mark

For hiking, how well a GPS can pick up the satellite signals in the woods / mountains can be an important issue…if you can’t get a strong enough signal to get a location fix, it won’t do any good. The ability to pick up the signals under tree cover seems to vary quite a bit from model to model.

For example, I have a Magellan GPS315, an about 8 year old 12 channel receiver. About 1/4 of the time it can’t get good enough reception in the woods when I turn it on to give me a location. Also, the initial location that it reports when turned on can be up to ¼ mile off from where it settles down, so I have to let it average for a couple of minutes to be reasonably sure the location data is good.

When hiking in the woods, I use my 60Csx along with USGS quad maps. While the trails may not be on the paper map, during a water or snack break it is easy to confirm where you are on the map. Make sure your GPSr is set to the proper datum and set it to display UTM coordinates. It is a snap to determine where you are. Some of the newer printed maps don't have grid lines on them so I bought rulers, pens, and various templates from: http://www.maptools.com/ I also have made topographic maps for my GPSr, but find it is easier to look at a nice big paper map. The combination of paper and GPS is great.

Depending on your brand of GPSr you may be able to download saved trails from other hikers. I was surprised at how many trails are available for download.

Is there a web page for exchange of saved trails? If not, maybe we should start one.

Of course, there is the question of trusting someone else's trail info!

There are several, though one that I've been the most impressed with is http://wikiloc.com with it's way cool Google Maps integration.

http://mapcenter.cgpsmapper.com/ has quite a few already made ready for download.

An interesting thing to do.. is to compare the Delorme TOPO (150K) Atlases that say "GPS Grids" with the older ones that don't.

The main difference that I see is the inclusion of GPS grids at one minute intervals. That's still a mile of variance for lat and long which probably will get you located and keep you from being really lost.

I'm not sure about UTM.. coords... I don't see them on the Delormes but yes on the USGS quads...

and yes.. the GPSr mapping units.. the maps are merely digtized versions of (hopefully) USGS source data.

but I'm glad to see the dialogue about how to plot lat/long on the paper map because while it is not rocket science.. it's not quite as trivial as it appears until one has tried to actually plot a lat/long on a map - and when you're actually out on a trail... and trying to navigate... .. say something simple like figuring out how far back to the trailhead... you gotta be able to locate yourself on that map.

good stuff! I too am appreciating the dialogue!

You might check out the new deLorme GPS. It comes with the deLorme Topo mapping program and you can download maps into the GPS. You can also load aereal (sp???) surveys into the thing.

DON

Another way to get map trails into your GPS:

Scan your paper map into a JPG file.
Pull the JPG up in GoogleEarth and wiggle it around until it fits over the GoogleEarth location (turn the map layer opacity down so you can see easier).
You can then trace tracks, insert waypoints, etc. Same the KML (GoogleEarth) file to your PC. Go to this site and it will translate the GoogleEarth file into a GDB file which can be transferred to your unit with the Garmin software.
I've done a bunch of trails for a lot of parks in Toronto, and southern Ontario with great success. I'm working on a full set of Bruce Trail maps at the moment.

http://www.gpsvisualizer.com/gpsbabel/


If you find it all too daunting, just scan the map and send it to me. I'll send back the tracks and waypoints for you.

It seems like choosing a detailled map source for accurate topos with trail info is as much, if not more important than the unit itself.

I find that having a full trail map on the receiver is helpful, but not truly vital.

First, I mark a series of significant points along the trail on a paper map, each with a unique ID. These include, depending on the hike, trail junctions, major turns, USFS gates, beginnings/ends of sharp ascents/descents, peaks, saddles, stream crossings etc. If the trail has a long segment with no major feature, I pick a point or two along that stretch too.

Then I open the GeoPDF that covers the area in Acrobat Reader. GeoPDFs are scanned (raster) and geo-referenced 24K quad maps free to download from store.usgs.gov.They are used with a free GeoPDF toolbar, available from www.terragotech.com. On the GeoPDF I set the same parameters as my MapSource (WGS84 and lat/lon as decimal degrees) and then, holding the paper map next to the screen, mark my waypoints. This gives their coordinates, which I then plug into MapSource and upload to the receiver. It sounds like a lot of work but isn't because there are usually c. 7-20 waypoints per hike. And it goes quickly once you start.

Note: with digital maps you don't have to use UTM, just make sure that all products you use are set to the same datum/coordinate system. UTM is only important for reading coordinates off paper maps (in this context). Google Earth, by the way, uses WGS84.

If you have a markable, receiver-usable 24K digital map, you can skip the GeoPDF step altogether and mark waypoints there directly. (Garmin's statewide 24K sets come on chips and are not [yet] markable on the computer. The National Parks & vicinity series is).

Thus, while hiking, the actual trail is not visible on the receiver but the key waypoints are. Since they are also marked on the paper map you can tell exactly where you are (beware of hiking without paper topos). In short, you don't really need the whole trail on the map, only key points along the trail. I hope this helps.

I have had excellent luck with my GPS and the DeLorme Gazetteer maps for my state.

I can easily match the GPS, Lat/Lon position to a place on the map and many of the state gazetteer maps have pretty good details and markings for trails and other points of interest.

At first I used just the GPS unit and found I was often very confused. After I bought the DeLorme Topo maps and learned how to see my position on the paper it all became very easy.

Keep in mind that a GPS can show you a direction to get to or from a point but it can't tell you the best way to proceed, Ie; a passable trail or route unless it has been there before or has the route pre loaded. While out in deep woods on our ATVs we rely heavily upon the track back feature because the ATVs can't climb cliffs or pass through deep water.

The old saying, "You can't get there from here" comes in to play with a GPS when it tells you your destination is straight ahead but there is a major cliff right in front of you.

Gary

Your last point is very important, Gary. Here is something related to keep in mind.

First, most topo maps were created before GPS. Updates to them are based on aerial photography, and natural areas don't receive the same type of ground-proofing as inhabited areas. Hence, away from habitation (and especially in forested landscapes), topo maps are generally accurate but not to GPS standards. Your receiver may reveal map features, even man-made ones, that are 30+ feet off.

Second, it is crucial to give verbal directions when sharing waypoints. GPS accuracy of +/- 20-80 feet is usually sufficient, but these distance make all the difference with features like cliffs or streams. You may share a waypoint you captured of a beautiful cliff vista point or a campsite along a stream without realizing that, given the said normal error, the point you gave is actually 30+ feet ahead of where you actually stood. Someone may plug it into the receiver and start walking, concentrating too much on the unit when getting close. This leads the person right to the edge of a cliff, or across a dangerous stream he doesn't really need to cross. If intending to share a waypoint in such areas, consider averaging for 10-15 minutes or include details along with the waypoint.

I encountered this last year in a forested valley in the Appalachian Mountains (Garmin 76CSx showed EPE of 21 feet). I stood next to a wide stream and marked a waypoint without averaging. On 24K digital maps, however, it looks like I crossed the stream, walked 30 or so feet on the other bank, marked a waypoint, then returned.

I do very much agree with you mesoplodon. Our entire GPS system is a tool worth having but certainly not one with pin-point accuracy.

I am not up to speed with the principals of OFF SET but understand they do infact exist. I have been quite satisfied with a term I call "Repeatable Accuracy" with my own units however. Once my unit has been to a place and established a route and waypoints along that route, I am fairly convinced that unit will bring me very close right back to those points. What I am not certain of is for how long those tracks/routes and waypoints will remain accurate.

On evening ATV adventures we have used our units to go to a particular fishing hole deep in thick woods. When returning from that evenings trip the track back feature appeared to be spot on and guided us over the exact terrain we had passed along on the way there. A few weeks later we attempted to use the same tracks and found them to be a bit off the mark.

My assumption here is that an exact coordinate given in Lat/Lon is not the same exact spot on the map on every day.

As you state, if I were to burry my mason jar treasure in the woods and mark the exact lat/lon position and then write it down for future locating, I will also need some specific land marks and exact triangulated measurements to be able to find it in the future.

Feel free to correct me where I am wrong with this.

Gary

No, for practical purposes a given set of coordinates will represent the same spot on the map from one day to the next. (You can neglect continental drift.) A more likely reason for the difference on the second occasion is that the satellite geometry was different from the original trip, resulting in a difference in the position computed by the GPS. It calculated its position to be on the original track, but the error in its computed position put it slightly off.

I am not sure what you are saying is correct and I am not sure what I am about to say is either!

I believe our military and other approved interests can use GPS with near pinpoint accuracy. For obvious reasons, I also believe there is an implanted off set that consumer products cannot correct which is causing the minor differences.

I may have said it wrong. The lat/lon position on a map does not change and is always the same. It is the lat/lon position on your unit that is different in that when it says you are at the exact position you might actually be between 30-80 feet off. I would be willing to bet if your hand heald was placed along side of a GPS in a commercial airliner you would have a rather large difference in the stated positions.

Gary

What you are referring to is Selective Availability. It was something the DoD implemented a number of years ago, I think in 1990, and Pres. Clinton cancelled it back in 2000. The signals we are getting now has a zero offset.

I know they are going to have a new satellite in 2012 that will have civilian code, and a new encrypted military code.



True. Our consumer GPS is not as accurate as a airliner GPS. However, it is really because by quality and cost. As an consumer, you can go out and buy a survey quality GPS, but you will pay dearly for the unit.

I would have to see this on that TV program " How they do that " to be a believer. I would expect a GPS for surveys to have a bit more accuracy but I also expect that our government has some control over the satellites and the signals they send to normal consumers Vs government and commercial interests.

I am not saying you are not 100% correct, just that I don't believe those who have control over the satellites want every GPS owner to have pinpoint accuracy.

Gary

As mentioned above there are several signals sent by the satellites. Prior to May 2001 "selective availability" degraded the accuracy of the civilian signals world wide but this can now be done by geographic region (for example in war zones). I imagine the others could be degraded too but that probably isn't necessary with the encrypted military signals.