Along the Hudson and a new GPS Receiver

In this post I'm going to touch on three regular topics for this blog:

• Hiking in Moreau Lake State Park (MLSP)
• Old Trees
• GPS Technologies

Looking across the Hudson towards the Palmertown ridge (and the main body of Moreau Lake State Park). Spier Falls Road is visible in the foreground on the far shore.

I got out yesterday (Jan. 18, 2016) for a hike on the east side of the Hudson River in Moreau Lake State Park (MLSP). Starting at an informal parking area on Call Street (between Queensbury and Corinth) this was a bushwhacking trip of just under six miles (round trip). Even so, it was a rather tough day. It was cold (mid-teens at best), the ground was covered with a layer of solid ice with an inch of snow on top and, and the route crossed a series of deep ravines cut by the streams that flow down from the surrounding hills into the Hudson. Only the last mile; from the point opposite the Sherman Island boat launch on Spier Falls Road to the Spier Falls dam itself was easy walking. Worth mentioning is that I could not have made this trip without the "micro-spikes" that I now carry on all Winter outings. These "boot chains" have exceeded my expectations at every use (available from many sources, here is one). 

The area in question is across the Hudson River from the main body of MLSP and it is little known and little used. Probably the best access is from Hawk Road (previous post here), but parking at Hawk Road is a problem in the Winter and it's a lengthy walk from there to the section east of Spier Falls dam. This area is not wilderness by any stretch, but it is wild and in places the terrain is very rough. There are numerous old logging roads and places once cleared for agriculture throughout this section and the foundations of abandoned structures are seen in several places. 

Foundation of an abandoned structure. The area around this foundation is relatively level and large enough for a field or pasture. The stand of same size trees indicates that this was cleared land in the past. Judging from the size of the trees, that was not the distant past. The agricultural use of this land was likely abandoned only in the past 30 to 40 years.

An ancient Maple

On the fringe of a once cleared agricultural area I came across a tree that has got to be one of the oldest in Moreau Lake State Park. It's a Sugar Maple (I think, mid-winter ID), and this tree is clearly in its twilight years. I didn't have my tape measure with me, but it is easily four feet in diameter. 

Sugar Maples can live to be over 300 years old and a tree of this size, with bark weathered and aged in this way, could be in that category.

This tree was located at the edge of an area that was probably cleared for grazing. And that's a common scenario for witness trees in the northeast. When the land was initially cleared trees growing along the edges of fields and pastures, and along stone walls, were left in place and became part of the agricultural landscape.

GPS - Garmin GPSMap 64S

One of my purposes for this outing was to put my new GPS receiver to the test. I've just purchased a Garmin GPSMap 64S. I've been thinking about acquiring a new GPS receiver for a while, but nothing I was seeing justified the cost. Then the clever robots at Amazon dropped an ad for the 64S on a web page I was viewing. At $230 the deal was too good to pass up.

Initial testing at Spa State Park over the weekend looked very promising, but I really wanted to put the unit through its' paces on a longer hike through a forested area. Not surprisingly, the 64S produces superior results on every front. For one thing, it's easier to use; no small consideration when it's 15 degrees with a stiff breeze blowing in your face. And while it is slightly larger and heavier than the eTrex it has a much better antenna. This is important when operating in thick forests and steep terrain.

It's not trivial to compare the accuracy of GPS units, at least not in the under $1000 dollar category where you have limited control over which satellites the receiver makes use of, but 64S has several features that should provide better and more consistent accuracy. The GPSMap 64 series receivers can make use of both the US GPS system as well as the Russian GLONASS satellites. All other things being equal more satellites should produce better results. The 64S is also capable of using the WAAS/EGNOS ground correction system. That's a big topic in its' own right and I'll discuss that further in a future post.

There are also a number of feature improvements, the most significant of which is that the 64S allows you to control the frequency at which it stores new locations when recording a track. This particularly useful when recording hiking routes. I set the 64S to add a new point to the track at one meter intervals; meaning that as you move along it stores one point per meter of travel (it can also be set to use a time differential). Set in this way you get a lot of data but it produces a much more detailed route than I could previously capture. This also avoids the annoying problem that I encountered with my older Garmin unit. When I would stop for a break, or for lunch, the older unit would continue to add points to the route based on a time differential (every 15 seconds would be my guess). So you would end up with a large number of points clustered around the location where you stopped. These could be cleaned from the data, but it was one more step in the process of producing a clean representation of the route.

I'm working on a detailed comparison of the performance of the 64S with my older receivers but the summary is that I don't know how I was getting by before.

Moreau Lake State Park, east of the Hudson River. The light blue line is my route. The heavy red line is the boundary of the section of the park that lies east of the Hudson River. Call Street is represented by the yellow line. The main section of the Park is on the west side of the Hudson, and Moreau Lake is just out of the area of the image at the lower right corner.

• Marker A: Parking on Call Street
• Marker B: Stream Valley
• Marker C: Spier Falls Dam
• Marker D: Sherman Island boat launch site on the west side of the Hudson (for reference)
• Marker E: The Hawk Road Area

You might notice from the map that I wandered outside of the Park boundary at one point. That was inadvertent. At that point along this route you have to get over a steep-sided gully. Steep enough that given the icy conditions it was a challenge to find a place to get across. Most of the year it would be easier to stay in the park and get through this section.

A Section of the route showing each point captured by the GPS. Click the image to see it at full size. The GPSMap 64S, set to add a point to the track at one meter intervals captures a highly detailed representation of the route. Map Images from Google Earth.

Bushwhacking Rules One and Two - The Woods Don't Care

As a loyal reader of this blog you know that when I go hiking I sometimes go off trail and do a bit of bushwhacking. I like to drudge up old and forgotten Adirondack routes and trails, and this fits nicely with searching around for patches of old growth forest or finding Beech trees that have BBD resistance. I commonly plan my routes so that my path at some point intersects a formal trail that I can follow out of the woods. Occasionally, when the trail I am seeking does not appear as expected, an alarming thought crosses my mind; "What if I cross the trail without realizing it?" This is usually accompanied by the even more disturbing thought; "What if I already crossed the trail and I'm heading off into the un-tracked wilderness? Oh no..." (then I recall that it is the Adirondacks, it might be wild but it is hardly un-tracked)

This has happened a few times but the the outcome has always been the same. Within a few minutes I step onto the the trail I was looking for. And this inevitably brings a smile because when you are bushwhacking even a lightly-used marked trail looks like a four-lane highway through the woods. From this I've developed a rule of thumb (Rule Number One of Bushwhacking); "You won't miss the trail, you'll spot it when you come to it, keep going." This rule has served me well because doubt can be a serious problem in its' own right. And doubt --edging towards panic-- has been the undoing of many a "lost" hiker or hunter.

This year I learned an interesting variation on my rule, which is; "you won't spot the trail if you are walking in the wrong direction." As you might imagine this corollary rule didn't appear out of the blue. I was attempting to reach Twin Ponds from the Thirteen Lake-Puffer Pond trail but tough conditions, and a late start, had caused me turn back short of the ponds. Heading back to rejoin the trail, which was less than a mile away, I decided to take an alternate route to avoid swampy terrain I had crossed on my way towards the ponds. After beating my way through rough terrain for nearly an hour I started to question my "rule number one of bushwhacking". The terrain didn't seem right and I really should have rejoined the trail by then.

I generally avoid using GPS for route finding but I had been recording my track using the GPS in my phone. So I pulled it out to have a look, and what I saw surprised me. If the GPS track was correct, I was going the wrong way. Only then did I pull the compass out of my pack and check my direction. Damn, I was traveling west when I wanted be going north. Correcting for this I came upon the trail after only a few minutes. I had been traveling parallel to it for some time.  And the first rule of bushwhacking was confirmed. No way I would have crossed that trail without knowing it. (smile)

There was a lesson learned from this. It wasn't just over confidence, heck I hadn't even considered the possibility that I might be walking in the wrong direction. It was really a combination of hubris and laziness; the source of so many disasters, big and small. It was heavy overcast that day so there was no sun in the sky to help stay me on course and I hadn't bothered to check my compass. So now I have a new rule --Rule Number Two of Bushwhacking-- check your compass even if you already know the direction you are traveling.

I almost always have a couple of GPS devices with me, so why not just use GPS for route finding and eliminate the guess work? For starters, all the experts say that you shouldn't do it. Guidebooks, DEC and ADK websites, articles in the newspapers about hiker rescues, etc, all warn against "relying on electronic devices" to find your way when hiking. But this advice runs counter to common experience. Most of the time any decent GPS device, either a dedicated unit or the GPS feature built into a smartphone, can provide your location within a few yards. So why not use them?

The problem is that there are a variety of ways for these devices to fail or to give you incorrect information. Usually at a most inopportune moment. Still, the warning should really be that you should not trust to GPS alone to avoid getting lost. If know how to use your GPS device, and how it can fail you, then your GPS device is another tool you can use for route finding. I was going to conclude this little tale by saying "here are all the ways that GPS can fail you in the field; I've learned them all first hand." But that would have been foolish, I'm sure there other failure modes that I have not yet discovered. So here are some of the ways in which GPS can fail you in the field.

1. Your phone probably has a useful GPS capability but you must enable the "Location" feature for it to work. Setting your phone to record your track is pretty easy these days but if location is off it won't work. A good App should warn you if Location is off but this warning is easily overlooked. A good practice is to check your track on the phone periodically to make sure that all is well. Otherwise you might find that (the electronic equivalent) of birds have been following you through the forest and eating the breadcrumbs you have dropped. 
2. Many people turn "Location" off because GPS puts a heavy load on your phone battery. My phone is over two years old and with "Location" turned on the battery lasts only six to eight hours; not enough for a full day of hiking. I carry a small auxiliary battery that I can use to recharge my phone in the field, but even this can go wrong. I recently returned from a trip to find that the track I thought I was recording ended 2/3rds of the way through the hike. At one point I had noted that phone battery was getting low and had plugged in the external battery. I had forgotten, however, that if the battery level in the phone falls below a certain level (10% I think) the phone disables the location feature to save itself (sort of HAL like). This had happened. The catch is that plugging in the external battery does not re-enable the GPS capabilities of the phone. So the later part of the track was not recorded.
3. The battery life of hand-held GPS units varies considerably and cold temperatures reduce the power output of all batteries. Lithium cells are much more effective in cold weather and should be used in GPS receivers. And, if you are using your GPS for anything more than amusement, you should carry spares (thanks Mom).
4. Anticipate that you will not have Cell service while hiking. The GPS in your phone will work because the GPS system does not rely on the cellular network. But this means that your phone will not be able to download maps while you are in the field. To see your location on a background map you must plan ahead and download the appropriate map imagery before you go. Otherwise you might find your phone showing your location as a dot on a blank background. It is surprisingly difficult to get the right maps onto many devices ahead of time so verify that you have the maps you need before you leave.
5. Beyond dead batteries and software failures any electronic device you take with you on a hike can fail. A common cause complete failures is having the device in your pocket when you wade into a lake or river and it's deeper than you thought. Oops.
6. Depending on where you are hiking you may find that your device cannot lock onto the GPS satellite network to give you an accurate location. Dedicated GPS units that can use both the US GPS network and the Russian GLONASS system are the best defense against this problem. The more satellites your receiver can use the better your chances of getting a signal.
7. Finally, there are a surprising number of ways for the compass feature of your GPS unit to be completely wrong. With practice and care you can get the correct heading from a GPS compass but I have learned to be skeptical of GPS-based compass readings.

The best hedge against all of these potential problems is to carry a standard compass, and the appropriate maps, and know how to put them to use.

Shanty Brook and Mud Ponds

Nestled into the southeastern corner of the Siamese Ponds Wilderness are two bodies of water called the "Mud Ponds". My 1994 ADK guidebook (Central Region) calls these two remote ponds "jewels in the forest" and the book notes that the ponds were probably named by guides who wanted to deter visitors to favored fishing ponds. That deception is no longer necessary. These ponds are not easy to get to.

The route to the Mud Ponds follows an old path into the Siamese Ponds Wilderness and that path, as described in the ADK guide, is well on its' way to being fully reclaimed by the forest. The route has not seen any trail maintenance in decades and whatever hiker traffic it does receive is barely enough to keep the way open. Past the first couple of miles constant attention is required to avoid losing the path and the last mile to the ponds has deteriorated to the point where it should be approached as straight up bushwhacking.

As mentioned, the trail to Mud Ponds via Shanty Brook is described in the 1994 edition of the ADK Guide to Adirondack Trails - Central Region trail guide. Using TopoView to look at USGS topographic maps of the area I see that the trail all the way to the ponds is not shown on large scale (1:24,000) topographic maps from the 1990s but it does appear on the 1994 edtion of the 1:100,000 Raquette Lake map. The first appearance of the trail is on the 1957 edition of the 1:62,500 Thirteen Lake map. So the trail first appears on a USGS map in 1957 and it is gone from maps published after 1994. But that does not mean that the trail had faded from all current maps. The trail does appear on a current edition of the Trails Illustrated Northville/Raquette Lake map. That map was apparently sourced from the earlier ADK map that came with the ADK guidebook (it replicates minor errors present on that map). Looking at a new and nicely printed map it's easy to make assumptions about the accuracy of the information. Maps, like all documents, fall out of date and sometimes even the best maps are just wrong. Something to keep in mind.    

The route overlaid on a recent USGS topographic map (Bakers Mills, 1997, 1:24000). The red line shows the route I followed and the purple line shows the route I would follow if I went back to try again. This map no longer shows a trail from the brook crossing to the ponds and to reach Mud Ponds you'll need to bushwhack that last mile. 

The first challenge in visiting Mud Ponds is finding the trailhead. If you take Route 8 from Wells the parking area is on the right about ten miles from the place where routes 30 and 8 split. It's a large paved pull off with two entrances so you can't miss it. Except that it looks like an abandoned rest stop and there are no signs. The ADK guide says that you should park in this lot and walk up Rte 8 for a couple hundred yards to a dirt road that leaves the highway on the river side. You certainly can do that, but you can also park on the dirt road itself. There are several primitive campsites and plenty of room for cars to be parked alongside the road.

From the entrance to the dirt road you need go only 30 yards before an obvious path down the steep bank is seen. The guidebook states that two cables were stretched over the river at that point but no cables are present. If you look closely, however, you'll spot a tree with clear marks where a cable previously cut into the bark. When the water is low the river can easily be waded at that point and the trail is clearly visible entering the woods on the far side. Alternatively, if you work your way upstream for 75 yards you'll come to a spot where you can have a go at rock hopping across. You'll need to be nimble to get across with dry feet. And those missing cables? They are lying in a tangle a few feet into the woods on the far side.

The trail is pretty good as far as the first vlei. It's about as remote a spot as you'll find anywhere for a walk of less than two miles.

The first stretch of trail is easily followed but narrow. Just push your way through the trees and shrubs that are rapidly filling in the corridor. You won't go far before you'll encounter the first of the dozens (scores? hundreds?) of downed trees that cross the path. Repeat after me, "over, under or go around; over, under or go around." This is a decision you'll make many times on this route. After a quarter mile the trail comes along side Shanty Brook and opens up a bit. At .6 miles you'll come to an obvious path leaving the main trail on the right (east side). The trail and the brook are separated at this point but you should be able to hear falling water. The side path leads a short distance to an overlook above the first of a series of falls and cascades on Shanty Brook. This falls is quite impressive with a 15 foot vertical drop into a rock walled chasm. The falls is well worth a look and a worthy destination in its' own right. But take care; the side path comes rather abruptly to to a vertical drop near the top of the falls. 

Falls on Shanty Brook. Looking down from the top.

The route beyond the falls continues to be easy to follow and at about 1.3 miles the path crosses Shanty Brook. Crossing the brook could be difficult in times of high water but few will actually face that challenge. If crossing the brook will be difficult then crossing the Sacandaga East Branch will be a much more significant challenge. 

At just under two miles you reach a large open vlei. This a pretty spot and it too could stand as a worthy destination. Past the vlei the path generally stays close to Shanty Brook as it meanders through a valley where many generations of beaver have dammed the stream. The path through this stretch remains generally easy to follow and in places where it fades a bit of searching should get you back on track. Someone has tied orange marker tapes to tree branches in a few places; perhaps to help them find their way back.

Looking across the first vlei towards the Blue Hills.

Past the first vlei the route stays close to the edge of Shanty brook. Recent beaver activity has backed up the stream in several places flooding the banks. Yes, that is the path disappearing into the muck. This is one of many places where you'll need to work around an obstacle and then try to pick up the path again on the other side. 

If you are aiming to visit the Mud Ponds you'll reach the critical juncture about 2.7 miles from the start. I didn't realize it at the time but when you reach the place where the path passes close to a solid looking beaver dam (at the lower end of another large vlei) you have reached the turning point. I continued northwest following a faint trail along the east side of the vlei. After a few minutes of walking, however, all traces of the trail faded away. This, along with the fact that I was bearing due north --not the expected direction-- led to the realization that this could not be the correct way. I knew that the route to Mud Ponds makes a 90 degree turn from northwest to southwest about 2.7 miles from the trailhead and I had clearly gone too far. Making my way back to the previously mentioned beaver dam it dawned on me that the beaver had flooded the place where the path crossed the brook and turned to the southwest. Crossing the brook below the dam I searched along the west edge of the vlei until I found a faint path emerging from the pond. That path looked promising but it soon reentered an area flooded by past beaver activity and was lost.

According to my map it's just over a mile from the turning point to the outlet of the upper pond (the point between the two ponds). I worked my way through the tangled forest mostly within sight of the stream/mud flats/vlei/beaver ponds for over an hour to reach a point where I could just see the lower pond through the trees. This route passes through a young second growth forest with a particularly dense (and annoying) understory. Looking towards the ponds all I could see was more tangled and swampy terrain so I called it a day and turned around. Whatever path once existed has been fully reclaimed by the forest and I make that statement with confidence because I expended considerable energy searching up and down the slopes trying to pick the up the path (with the hope of easier going). And you can find faint remnants of a path. There are several places where a distinct footpath can be found and followed. But in each case the trail is soon lost in tangles of blow down or where beaver activity has flooded the way. So, despite what you might see on a map, there is no trail from the stream crossing to the Mud Ponds.

I may go back some day and the knowledge of what to expect will make it much easier to reach the ponds. I'll probably climb up the slope of Blue Hills Mountain a short ways and head straight for the outlet of the upper pond. Contouring around the shoulder of the mountain will add some climbing but it will reduce the distance and it will (hopefully) avoid the worst of the tangles.  Treat this section of the route as pure bushwhacking and pick the path of least resistance. Attempting to follow the old trail requires extra effort for no significant benefit.

The Pine Orchard: You Know When You Are In It

The Pine Orchard is a well known stand of old growth White Pine and Hemlock near Wells (NY). If you read this blog you know that I'm always on the look out for the big old trees, so a visit to the Orchard was long overdue. I'd read that the Pine Orchard contains trees up to seven feet in diameter but, I have to admit, I was skeptical. I wondered if trees, like fish, get bigger with each telling of the tale. I was prepared to be underwhelmed by the Pine Orchard. Happily, I was wrong. The Pine Orchard is impressive and these may very well be the largest and oldest trees in the southern Adirondacks.

But how big --exactly-- are the pines in the Pine Orchard? I measured a few trees and the largest one I found has a diameter of 51 inches; just over four feet. I took this measurement by stretching a cord around the tree four and a half feet above the ground. The distance on the cord measured 161 inches and dividing that by 3.14 yields the diameter: 51 inches. That's not the six to seven feet that some have reported but I might not have measured the very largest trees. And while measuring the diameter at four and half feet is standard practice in forestry circles, others might have done it differently.

I'm interested in the history of the Adirondack forests and the large old trees have stories to tell. So I look for them when I hike. Over the past several years whenever I've spotted a large tree I've noted the location and estimated the size. Now that I've refined my measurement technique I see that my past estimates may have tended towards the high side (No, Dad, this does not apply to fish I've caught in the past). I carry an old ski pole as a walking stick and I've used the pole as a gauge for estimating tree diameters. I now see that this technique is insufficiently precise. In the Adirondacks, trees with diameters of 36-40 inches are found in many places. Trees of that size will typically be more than 125 years old and a stand containing many trees of that size may have been passed over, or selectively logged, in the first wave of industrial logging. That first wave took place after 1850 and continued into the early part of the 20th century. You can also find trees with diameters larger than 40 inches scattered about in the Adirondacks, but these are much less common. These trees were almost certainly standing before 1850. The really big and old trees, with diameters of 44 inches or larger, are rare. The Pine Orchard contains a number of trees in the 44-48 inch range and estimates that I've seen place the age of the stand at over 200 years. (Note: the correlation between tree size and age varies with species and growing conditions).

Image One: A large White Pine near the point where you first reach the Pine Orchard Stand. The strand of yellow yarn is one foot in length.

The Pine Orchard: Old Growth Forest

The Pine Orchard is old growth. At 200 years without external disturbance the forest has reached the climax stage in terms of ecological succession. For this location, and given whatever circumstances protected it originally, that means mature White Pine with some Hemlock and a few old hardwoods mixed in. Stands of old growth pine are often compared to a cathedral and that description applies to the Pine Orchard. The forest floor is blanketed with a deep layer of pine needles that absorbs sound and this is an airy, quiet, place. I was there on a very warm day and it was pleasantly cool under the cover of the large trees.

Image Two: The cathedral in the pines. The forest floor is covered with a two century accumulation of pine needles. Smaller trees are mixed in but the canopy is dominated by the large White Pines.

The Trail and the Hike The route I followed leaves the Pumpkin Hollow road at the Murphy Lake trailhead. As with the the trail to Wilcox Lake this route is marked and maintained as a snowmobile trail. The 1994 ADK guide to Trails of the Southern Region described this trail as indistinct and hard to follow. That Guide advised that this route should be attempted only by hikers skilled with map and compass and it went so far as to say that the trail was not recommended for parties of fewer than three people.

Image Three: From Google Earth. The entire route covering 5.9 miles each way.

That guide was written over 20 years ago and much has changed. I don't know whether the warning was justified when the book was written, but it is not true today. The route generally follows old woods roads and it for pleasant walking. There are a couple places where arrows (signs) point the way. Not because the trail is indistinct but because multiple old woods roads intersect and it could be difficult to pick the correct route. Interestingly, the warning from the ADK guide was carried over to a much newer map. My favorite trail maps these days are the "Trails Illustrated" Topographic Maps produced by the National Geographic Society. The Northville/Raquette Lake map covers the southeastern Adirondacks and that map restates the warning about parties of "at least three persons" word-for-word.

There is also a meaningful discrepancy in the length of this route as stated on signs and as printed in various guides. As measured using GPS my hike covered a total of 11.8 miles. This included a bit of wandering around so the sign board at the road which states the distance to the Pine Orchard as 5.6 Miles is reasonably accurate. The 1994 ADK Guide lists the distance at 6.6 miles one way. And a third distance, derived by adding up distances seen on signs along the way, yields a total of 4.2 miles. Applied to the round trip, the difference between the shortest and longest mileage is over four miles. That's a serious lack of accuracy.

There are two apparent sources for the uncertainty. The first is that there is no distinct point or boundary to mark your arrival at the Pine Orchard. The lack of a clear "here it is" location accounts for a tenth mile or two of the discrepancy. This is a question of precision. Lacking a distinct end-point it's difficult to measure the distance to the tenth of a mile precision typically used on trail signs. The second consideration is that over the past 30-40 years the trail has been re-routed, probably more than once. The 1994 ADK Guide alludes to this noting that the trailhead had been moved to avoid a crossing of private land. This is also evident in an old sign seen at the junction with the Flatters trail. The sign says that it is 2.6 miles to the "Willis Lake Road" but the trail doesn't go to the Willis Lake Road. That was probably the original starting point. If the sign stated the distance as "a few miles" it would be more accurate but not very precise. As it sits, it is neither.   

Image Four: Stanton Miles: When our children were young we would take them hiking and the first thing they wanted to know was; "how far is it?" To which I would respond "a couple of miles." It took only a few outings for them to realize that my "couple of miles" could be anything from two to five miles. That answer is accurate but not very precise and my scale became known in the family as "Stanton Miles." If you use Stanton Miles the difference between what appears on the sign and the actual distance of four miles is accounted for.

Uncertainty, Accuracy and Precision

Measuring the diameter of a tree is pretty easy. And collecting measurements from many trees is a straightforward process:

• Measure the tree
• Record the location
• Record the species
• Note unusual or complicating factors
• Repeat

That sounds easy enough, and it is easy. Which is why I am continually surprised by all the different ways that uncertainty creeps into the data. Part of it comes from doing this work in the Adirondack Biting Insect Preserve. During the warm months you encounter many many small complications and distractions and for the rest of the year your fingers will be numb making it difficult to write out notes. But sometimes I run into more specific issues:

• Diameter: What about double-trunk trees? Or trees in difficult locations? What if there is a branch or some other oddity at the 4.5 foot height where I want to measure?
• Location: Assuming that the accuracy level of your GPS device is good enough, and assuming that you have a good signal from several satellites, and assuming that you correctly note which location goes with which tree, it nothing more than the push of a button.
• Species: I'm familiar with most tree species seen in the Adirondacks, especially the species that get to be big. Still, when I have gone back and looked at the same trees a second time I've found that I get some of the them wrong.
• Notes: Some days I do a good job of recording the unusual or complicating factors and some days not so good. And this information often turns out to be important when trying to draw conclusions from a body of data.

On one point I have no doubt. All non-trival data contains errors and considerations of precision and accuracy are relative to the intended use. These are the sources of uncertainty.

A Couple of Miles: I was just being accurate

As often happens, the use of a tool under less than ideal conditions leads to a deeper understanding how the tool works. Using GPS to record locations and to record the tracks I've follow has given me a deeper understanding of how the system works. I'm going to return to this topic in the future but a few key points go right along with the theme of this post. First, take a look at image five. The lines show a short section of the track captured by my GPS receiver on the hike to the Pine Orchard and back. The line on the left was from the inbound leg of the trip and the line on the right is from the return trip. I walked the same path both ways so it's odd that the the lines are so far apart. To get to the bottom of this you need to know something about how I hike.

I took much longer to complete the trip to the Pine Orchard then I did on the return and this is typical for me. And this was not because of the terrain. The route crosses a couple of small ridges but there is very little difference between the elevation at the turn around point. It's counter intuitive, but I typically travel at a slower pace on the way in because I'm fresher. On the way in I stop to record measurements, I take photos and I generally take more time to enjoy the forest the scenery. On a hike of this distance by the time I'm half way back to the car I'm starting to get tired. And this is the counter-intuitive part, I tend to walk faster and I move along without stopping. On this particular day, it was hot and by the time I reached the area shown in image five I'd been hiking for over five hours. It was also into the early afternoon and I was I not hiking alone. I was traveling with dozens of new (and now really annoying) friends that I'd made along the way. Deer flies, midges, mosquitoes and a few too-stupid-to-just-give-up-and-die black flies. The bug spray that had been mostly effective earlier in the day was no longer working. 

Image Five: GPS Accuracy 
The lines in the image show a short segment of the track captured by my GPS receiver on the hike to the Pine Orchard and back. The line on the left was from the inbound leg of the trip and the line on the right is from the return trip. I was walking on the same path for both legs of the journey, so you might expect the lines to be very close to each other. (Map Image from Google Earth)

A GPS track like the one shown in the image is recorded as a series of points. Every second or so (this will vary based on the device) the GPS receiver calculates your location and stores the coordinate pair representing that location.  When you stop the receiver gets extra time to correct for errors so stopping periodically improves the accuracy of the track overall. This is especially true when walking through a dense forest where the strength of the signals is reduced by foliage. In image five I added a note to a place where it looks like I took a short side trip off the trail. But I know that that never happened. What did happen is that the GPS recorded a couple of points with much lower accuracy and those points became part of my route. If I was planning to use this track as data I would need a method to clean up these kinds of errors. 

There are many factors that limit the best case accuracy of GPS. A GPS receiver captures signals sent by satellites orbiting the earth and when the receiver has signals from at least three of these satellites it can calculate your location. The U.S. GPS system uses a constellation of 32 satellites positioned so that there should always be at least three satellites above the horizon and "visible" to a GPS receiver located anywhere on the earth. Under good conditions a typical consumer GPS receiver can fix your location to within about 10 yards -30 feet- using signals from three satellites (four are required to also calculate your elevation). At that accuracy level you use the coordinates calculated by the receiver and place a point on a map. Then you draw a circle with a diameter of 30 feet around the point. Your actual location lies somewhere in that circle. 

Depending on what you are trying to do that may or may not be accurate enough and it's usually possible to get much more accurate data. For instance, it's common for there to be more than the minimum of three satellites available to your receiver. Modern GPS receivers including the ones found in most smart phones, use the "extra" satellites to average out some of the errors that otherwise limit GPS accuracy. For example, when I save a waypoint (the coordinates for a single location) using my Garmin GPS it tells me how accurate the fix will be based on the set of satellites available to it. The use of additional satellites and averaging commonly improves accuracy into the ten to twenty foot range. On the other hand, dense foliage, cliffs, mountains and other obstructions reduce accuracy or prevent the receiver from getting any fix at all.

The point is that data taken from measurements is always uncertain to some degree and the level of uncertainty varies based on the specifics of how you gather the data and your intended use. You have to ensure that your data is accurate enough for the intended use and you have to avoid mis-representation by overstating the level of precision. When I use a cord to measure the circumference of a tree, if my measurement is accurate to within one inch then I can state the diameter in inches. Dividing the circumference by Pi to get the diameter will almost always yield an answer with a remainder, something like 45.3. But the .3 must be thrown away. The accuracy level of my measurement does not support that level of precision. If a trail sign states a distance as 2.6 miles, then assuming typical rounding to the nearest tenth we can say that it's accurate if the actual distance is between 2.55 and 2.65 miles. Assuming, of course, that it's the correct sign for the trail you are on. My GPS gives me coordinates with 6 decimal places of precision. That's precise enough to separate locations that are just inches apart. But the device is not nearly that accurate and the last digit (and maybe the last two) should be discarded. The extra precision is meaningless at best and misleading at worst. Whenever we take measurements there is uncertainty and the level of precision we use should not overstate the accuracy of our technique. 

You see kids, when I said it was a "couple miles" I was giving you the most accurate answer that I could.