peter

Generally, the contour interval for a given map series varies depending on the type of terrain in an area. That's true of the USGS 1:24000 series and also for Garmin's topo maps. E.g. their Topo24K series has contour intervals of 10' in the Minnesota Boundary Waters area but 40' in much of the Grand Canyon. Of course with DEM digital encoding of the elevation data the software can give you any contour interval it wants to even if the level of detail doesn't really warrant it. So just looking at contour interval as a measure of quality may not be giving you anything meaningful.

The basic yellow eTrex will work fine for geocaching. Since it doesn't display a map it would be helpful to have some decent paper maps of the area. As BlueDeuce indicated, having a computer cable for it is very useful so you can download cache locations and also for lots of other applications (plotting your tracklog, keeping records of previous trips, etc.). But even if you don't have one for your eTrex, they're quite inexpensive (the eBay store of GPSGeek sells them for under $10).

The microSD card is a pretty big deal. In addition to letting you load more maps it also allows saving an essentially unlimited length tracklog and large collections of custom POIs. Furthermore the Cx model uses the SirFStarIII chipset which has substantially improved sensitivity to the Garmin chips in the C model and the processor seems to be quicker at tasks like redrawing the screen. The reduced battery life is presumably the result of the GPS chipset and processor change. Overall the Cx looks like a major step up from the C model.

No single device is perfect for everything. But the Garmin Quest models are pretty good for both driving (spoken directions, automotive mount/charger/maps included, charge while driving) and handheld use (decent life per charge, easily pocketable, waterproof and reasonably durable).

It's actually the ephemeris data broadcast by the satellites which is used for the position calculation (the almanac is the less precise data that's just used so the receiver knows which satellites are in view). But you're missing the key point that this still doesn't let the receiver know the distances directly. Sure it knows the exact time the signal was sent, but since it doesn't have its own atomic clock it doesn't know exactly when it was received. That's why GPS documentation always talks about 'pseudo-ranges' as the receiver doesn't know the real ranges until it has solved for all four variables: lat, long, elevation, and time (technically the three space variables are based on the ECEF [Earth-Centered, Earth-Fixed] coordinate system but the principle is the same). To do that absolutely does require that the receiver either get signals from four separate satellites or make some assumption about one of those variables; and the assumption that's used (in 2D mode) is that the altitude hasn't changed since the last position fix. To do any cross-checking and validity checking requires that you have *more* than four satellite signals. No, what it's "losing" is reception of the fourth satellite. With only three satellites (or sometimes even with four but a poor geometry), there is no way for the receiver to continue to calculate all three space dimensions plus time. The 2D mode works pretty well in most cases, but in situations where you actually are changing altitude rather rapidly you'll see your calculated horizontal position start to drift away from reality. The receiver is still trying to calculate your position based on the satellite signals and *assuming* a fixed altitude. If the assumption is wrong then the results of the horizontal position calculation will also be wrong. That would be ideal, but that requires always having four satellite signals so you can solve for those '4D' unknowns. The designers recognized that often only three satellite signals might be receivable. Rather than giving up altogether under those circumstances it's better to give a reasonable estimate of the horizontal position using a best guess for the altitude. That eliminates one of the variables and therefore lets you calculate the remaining three using data from only three satellite signals.

Using CitySelect-NA maps it'll be enough for street-level detail down to residential streets and rural lanes for almost half of California. Many smaller states could fit entirely or even several at a time. Where are you located - then we could give a more relevant example.

Garmin will repair it (probably actually replace it with a new or factory reman. one) for $99. Check their website for out-of-warranty repair. Not cheap but better than $160.

True for MetroGuide-USA versions 4.01 and 4.02, but not for the "and earlier" since MG-USA v3.0 (data version 2.0) didn't support auto-routing at all, not even on the PC. The current version of MetroGuide-Canada using DMTI data also supports auto-routing both on the GPS and PC.

Just a little nit with the above. Since our receivers *don't* have atomic clocks, they don't actually know the radii of the circles you've shown, only the differences between the radii. I.e. the receiver knows that it got a signal from Sat. A precisely so many microseconds before it got a signal from Sat. B, so it can calculate how much closer it is to A than to B but it doesn't directly know the distance to either one. Therefore just getting signals from 3 satellites isn't enough to narrow things down to 2 points. In your drawing think of changing the radii of all three circles by the same amount. In that case they may still intersect at two points, but not the same ones as before. The receiver would have no way of knowing which set of radii to use so with only three satellite signals there would be an infinite possible number of intersection points. An additional signal from a 4th satellite is required so the receiver can solve for its lat., long., elevation, and time. Alternatively, the receiver can make the assumption that it already knows the altitude from a previous measurement (usually not a bad assumption since we don't readily change our altitude rapidly). In that case instead of using a sphere from a 4th satellite it can use the surface at the assumed elevation over the earth as the 4th surface and determine the intersection point of it with the three spheres centered on the satellites. That's why the receiver can give a "2D" solution based on only 3 satellites but needs 4 for a "3D" solution.

Ask them here and I'm sure you'll get enough answers. It's not clear why you're having reservations about the V as a geocaching tool. Its main limitations are limited memory for storing enough maps for long trips and a PC interface that's slower than USB - neither is usually a problem for geocaching.

I did get confirmation from Garmin that the GPS-18/nRoute bundle would also allow me to use the CitySelect-NA maps with one other Garmin GPS. I ended up buying another GPS/CitySelect package which also allowed me to get a second unlock for my earlier GPS. But it wouldn't hurt to get a direct confirmation from Garmin yourself. $99 sounds like a good price from what I've been seeing, and yes, for the 60cs you definitely want CitySelect over Navigator.

Here are a few sites that have Garmin-compatible free maps: http://home.wtal.de/noegs/freemaps.htm http://rwsmaps.griffel.se/ http://www011.upp.so-net.ne.jp/mametaro/kanto-e.html http://www.elsinga.net/maps.html http://www.aracnet.com/~seagull/ORTopo/ I think these are all for letting others have access to some specific maps rather than also allowing uploads of additional shareable maps. But I'm concerned that spreading out the maps among more sites will reduce their usefulness. Here's the item from the MapCenter FAQ on the compiler features: "Q: What are the advantages of the online compiler? Is it better than freeware/shareware cGPSMapper? A: In addition to all features of freeware version, online compiler supports all features available in registered shareware version (city and POI indexing, additional city information: country and region, additional POI information: country, region, city and description), some features of the standard version (direct support for ESRI format, irregular map bounds, not limited city and POI indexing, full POI address and additional description), some features of the professional edition (building numbering, searching for address, searching for intersection) and even routing (with some limitations)."

There are already too many sites setup for the sharing of maps. The result is that they're scattered all over and not nearly as useful as a more comprehensive collection in one or at most a few spots. And there are some advantages in using the cgpsmapper compiler available at that site that provides features beyond those in the free/shareware versions.

Orienteering clubs frequently have topo maps of their local areas that are far more detailed and up-to-date than the USGS 24K series. But I'm not familiar with the Fletcher, VA quad and whether any clubs have already mapped that area.

Having seen how they're put together, you won't find that in any eXplorist. Would you call the explorist fragile? No, but from what I've seen neither the eXplorists nor the eTrex series is built as solidly as the old II/III+/V family.

Having seen how they're put together, you won't find that in any eXplorist.

Nor do they provide autorouting unless you also buy DirectRoute for more $$. The lowest price with autorouting I can think of is the GPS V/CitySelect package which is available for under $200 and I've sometimes seen the Quest/CitySelect for about $300. Neither has a magnetic compass

Why not use the MapCenter site that was linked earlier: http://mapcenter.cgpsmapper.com/ That's already set up just for this purpose and would make the maps available to more people. A note in this forum when maps are added would also be helpful to the geocaching community.

They're very similar and both will work ok and give you auto-routing in the Legend Cx. If you're going to just use the included 32 MB microSD card then the smaller regions of CitySelect would be a major advantage. But if you're going to get a larger card anyway (recommended), then I'd go with CityNavigator - slightly better routing data and turn descriptions and more efficient when loading very large map areas.

AFAIK you won't be able to create a routable version of the edited map unless you get the pay version of cGPSmapper. I don't think the free and shareware versions support routing. I second NeoGeo's recommendation to inform NavTeq about the bridge error. If we all do the same in our local areas the maps will become more useful for everyone.

It can certainly be worthwhile to have both and you can easily switch between them on the GPS (I frequently use the streetmaps to get to a trailhead and then switch to Topo to see the trails and contour lines). CitySelect/Nav. does include quite a few small country roads and is generally much more up-to-date than USTopo, but it won't always have as many dirt/gravel roads. Check it out using the MapViewer on Garmin's website at: http://www.garmin.com/cartography Zoom way in on a few areas with which you're familiar and see if the detail level is worthwhile. Having CitySelect/Nav on a 60csx also makes it much more useful for everyday activities around town and on trips.

Either CitySelect-NA or CityNavigator-NA will work fine and provide auto-routing with your LegendCx. They differ mainly in how the map regions are divided with CN having larger map chunk than CS. If you're planning on just using the microSD card that comes with the unit then CS would be preferable, but if you planned to get a bigger card anyway then I'd go with CN instead.

Now the blue circle. Well since no one knows exactly how its read or numericaly what it means its even more useless than I thought. I'm not sure how you got that conclusion from what I wrote. The total uncertainty in your position as shown on the map is the statistical combination of two sources of error: the GPS measurement uncertainty (Ugps) and the map uncertainty (Umap). Since these are statistically independent they should add in quadrature: Utotal = radius of circle = SQRT((Ugps)^2 + (Umap)^2)

The color screens themselves use very little power, at least those in the newer Garmin models. They get significantly better battery life than the previous similar models with grayscale screens. Any unit will use more power when the backlight is left on much of the time, but my experience with the Garmin color models is that the backlight isn't needed in most outdoor conditions when it's reasonably bright out. So if you're looking at a unit like the LegendCx that can run for about 30 hours on a pair of alkaline cells then it isn't drawing much current and the capacity advantage of the Energizer lithium-irondisulfide cells is fairly modest (usually less than 50% better). That's not enough to justify the much higher price unless you need the light weight or cold temperature advantages.

The GPSMAP 96C is waterproof (Waterproof: IEC 60529 IPX7 standards (submersible in one meter of water for up to 30 mins.) As are the other portable aviation models from Garmin; the 96, 196, 296, and 396. All meet the IPX7 waterproof specs. Of course I wouldn't want to take the larger ones backpacking anyway.