map making question

[the starchild]

i am working on my own map of monadnock showing points of interest, old trails and having nice contour lines. hopefully the final product will be 18 x 18.

the AMC map has all trails perfectly placed on the map using GPS but useless contour lines.

the really old USGS maps online are beautiful and have amazing contour lines, but no trails.

i am working on overlaying the trails of the AMC map on the old map, but things do not match up. If i make both maps the same size referencing the scale of miles on each it seems like things aren't right. features do not match up.

if i size the maps according to the relation of features such as the summit, halfway house road, monta rosa, pumpelly trail, then i must ignore the scale of miles not matching up.

sooo, my questions incase i have found new ways to bend the map:

is it likely maybe the scale of miles is wrong on one of the maps?

is it wrong to assume that if both maps are scaled to the same size, eveything should line up pretty easily?

what's the x factor here? something must be wrong?

thanks for your suggestions.

 

[Puck]

Are most of the AMC maps based on the 1959 series USGS maps that were generated by arial photos as well as GPS overlay?...that is someone hiked the trails with a GPS system backpack that took a reading at certain intervals.

It is interesting to see that you are showing a discrepency.

 

[DougPaul]

i am working on overlaying the trails of the AMC map on the old map, but things do not match up. If i make both maps the same size referencing the scale of miles on each it seems like things aren't right. features do not match up.

if i size the maps according to the relation of features such as the summit, halfway house road, monta rosa, pumpelly trail, then i must ignore the scale of miles not matching up.

My guess is the second method is more accurate.

You can determine the final scale by measuring the distance between two points on an accurate map (eg USGS topo) and using that on the new map to determine the scale.

sooo, my questions incase i have found new ways to bend the map:

is it likely maybe the scale of miles is wrong on one of the maps?

is it wrong to assume that if both maps are scaled to the same size, eveything should line up pretty easily?

what's the x factor here? something must be wrong?

Welcome to cartography.

In general, for two small area maps, you can have trapezoidal distortion (ie a square on one will map into a trapezoid on the other) plus offset. Simple scaling can only map a square into a differenct sqare. Independent scaling in NS and EW can map a square into a rectangle. And, of course, one can also have rotation. In general, if you locate 4 separate points on both maps, you can compute a transform which can handle all of the above.

The above assumes the conversion is the same for all points on the map. (Think of printing a map on a rubber sheet and stretch on end. The mapping equation between the two maps would then be different at different locations.)

If you get into large area maps, then you have to worry about the projections (the method used to map the surface of a sphere onto a flat piece of paper).

Doug

 

[TCD]

If it's a question of cartography, I'd be more inclined to trust the data from the USGS than from a recreational organization which does not have cartography as their prime mission. From my experience, I have never encountered a serious deviation in the USGS topo maps in the Adirondacks, but have often encountered trails drawn in by ADK not being exactly where they are drawn. (Trails move quickly and often, too, whereas geomorphological features move much more slowly). If old and newer USGS data disagree, then it may be a matter of methods changing over the years (aerial photos vs. satellite, etc.).

 

[Pete_Hickey]

From my experience, I have never encountered a serious deviation in the USGS topo maps in the Adirondacks,

Nye on the Metric maps. Real bad. In general, the metric maps are sloppy.

 

[arghman]

i am working on my own map of monadnock showing points of interest, old trails and having nice contour lines. hopefully the final product will be 18 x 18.

cool!

I've been doing a little introductory gis stuff from time to time, I would agree with DougPaul in that if your source maps use different projections, then you've got warping issues (bleah!) to deal with.

I don't know whether the new AMC maps have used GPS (probably one excuse Larry Garland has for redlining ) for finding trails, or whether it uses aerial photography. They may be off slightly on small-scale things.

 

[AMF]

I don't know how old your USGS map is, but the older ones (that had the nice shading) have been known to have substantial errors. I've seen some from the northeast with whole sub-peaks misplaced.
(as an aside, I have one framed - ordered a 15' map for a WVa quad direct from USGS back in the late 70's, & received an original 1909 edition on a light tan clay paper, with that nice shading. Beautiful map!)

 

[TCD]

Pete, you're right about the metric maps. I don't care for them. I think they have been "computer smoothed." The older english maps were drawn with input from field checks, and cliffs and other features were often drawn in based on the filed info. I think that info is getting lost in the metric maps.

 

[RoySwkr]

You need to get Allen Chamberlains book from the library and look at his trail map. Some of those trails are long gone and others surrepticiously maintained.

Supposedly the AMC trail maps were done with GPS but only some by LG personally, there are some real boners such as Davis and Owls Head. And they only did trails and got brooks for instance from USGS so they can show the trail on the wrong side of the brook and still have both features within acceptible error.

The newer USGS maps were made from air photos but only a limited amount of field checking done, that's why a lot of them are still "provisional". Depending on the terrain, it can be easy or hard to spot a trail from the air as you've no doubt seen looking from viewpoints.

 

[LenDawg]

Best book I ever saw on maps is Nathaniel Bowditch's American Practical Navigator, which is primarily a marine navigation book, but it gives a phenomonial mathmatical description of the different types of projections for chart making.

 

[arghman]

And they only did trails and got brooks for instance from USGS so they can show the trail on the wrong side of the brook and still have both features within acceptible error.

That I would call an unacceptible error, I don't care if the trail and brook are off by 200' in absolute terms but I'd like to know how many brook crossings and where they are.

 

[the starchild]

thanks for the beta y'all. there are some things to consider i didn't have any clue about. thanks for the homework assignment. warping and projections?!?!? yummy

i've been working and packing (moving to new apt.)this week and haven't had much time to mess around on the computer too much.

i did spend some time and it seemed like by matching up the mile measurements to size each map the same; the halfwayhouse road and main road are in different spots, but most of the mountain features match well, like the summit, minor summits and pumpelly ridge. so maybe its just the roads that are off?

i haven't seen the Allen Chamberlain book, but will have to hunt it down soon as several people have recommneded it. i didn't know it had a map in it. I have another SPNHF book called, The Monadnock Guide, which mentions many old trails, features and has a few maps. it is these maps i want to combine with the others to make myself a sweet little map for whacking and finding stuff.

 

[DougPaul]

i did spend some time and it seemed like by matching up the mile measurements to size each map the same; the halfwayhouse road and main road are in different spots, but most of the mountain features match well, like the summit, minor summits and pumpelly ridge. so maybe its just the roads that are off?

Remember that only certain objects can be identified and located accurately from aerial photos. These should be most likely to be consistent across maps. Other features (eg trails) involve a lot more guesswork and are likely to be less accurate. The inaccuracies are generally unnoticed by users until they compare two maps very carefully or start carrying a GPS around with them. Also many maps are produced by copying another map and then modifying the copy, so some features may have consistent, but inaccurate locations.

Try Terraserver http://terraserver-usa.com or Google maps http://maps.google.com/ if you would like to look at aerial photos with co-located maps.

IIRC, when the AMC started locating trails by GPS, they discovered that many of them were located inaccurately on the maps--trails can be very hard to see through the treetop canopy.

One other thought: how were these maps digitized? (If I can presume that you are working with digital maps.) It is always possible that there was some distortion in this process. Eg: paper changes size with humidity or can be stretched, optical system distortions, etc.

Doug

edit: erroneous statement about the Wasburn Mt Washington Map removed.

 

[Mohamed Ellozy]

IIRC, when the AMC started locating trails by GPS, they discovered that many of them were located inaccurately on the maps--trails can be very hard to see through the treetop canopy.

The June 2001 issue of Appalachia has an excellent special section section entitled "Mapping the Mountains: The Artful Science of Cartography", describing Larry Garland's work and putting it in the perspective of what one author called "5,000 years of map-making". The issue has one figure (p. 97) showing the location of trails around Crawford Notch from both the USGS and the new AMC maps; there are discrepancies but much less than I would have expected.

One article in that issue ("A Thumbnail History: How Maps got Here from There") describes (alas, too briefly) the surveying techniques used to plot trails in the pre-GPS era; hard work but capable of considerable accuracy.

(BTW, the trails on the Washburn map of Mt. Washington were all GPSed.)

No, they were surveyed (over a ten year period, 1978-1988) by conventional methods (if you consider laser distance measuring a "conventional method"). Alan A. Smith, one of the principals in the project (the other three were Bradford and Barbara Washburn and Casey Hodgdon) wrote a two part article on the project in the December 1990 and June 1991 issues of Appalachia.

 

[RoySwkr]

That I would call an unacceptible error, I don't care if the trail and brook are off by 200' in absolute terms but I'd like to know how many brook crossings and where they are.

I agree with you, and the way to make it work is to take GPS points at each crossing and note them in a log. As you can see by the maps this was not always done. And somebody needs to ask Larry Garland why the maps shows trails to Owls Head and Davis that don't exist if these are really GPS readings and not cartographers additions.

No, they were surveyed (over a ten year period, 1978-1988) by conventional methods (if you consider laser distance measuring a "conventional method").

They also used a tape measure! One winter day on the Crawford Path, B&B were measuring the length of the trail which is not on the map but they wanted to give a distance for it. (Tape pulls easier on snow.) B got cold and went back so I helped B on the windy section nearing Mt Pierce. Just before the trail junction the snow was so deep that we couldn't tell which side of a scrub patch the trail went on. Although the difference in measurement would have been only a couple feet, B decreed that he would come back in the summer to do that piece.

 

[Jazzbo]

Good link on USGS web site

The following link on USGS web site provides brief historical perspective on evolution of Topo map techniques. Original topos were made by surveyors who climbed up to prominant peaks etc and set up plane table survey instruments. In forties aerial photogramettry became the standard. Today computor and satillite techniques are taking us to levels of accuracy and digital communications.

http://erg.usgs.gov/isb/pubs/booklets/topo/topo.html

 

[the starchild]

Thank y'all for the history lesson and links. This is good stuff.

One other thought: how were these maps digitized? (If I can presume that you are working with digital maps.) It is always possible that there was some distortion in this process. Eg: paper changes size with humidity or can be stretched, optical system distortions, etc.

i am using an 1898 USGS 12minute quad map from this site. The maps have been scanned in quarters. To get the trails in the correct place i want to use the AMC map. I am not sure sbout the details of how the maps were scanned etc etc.

i prolly should try to overlay the trails on the TOPO (the softwaremap thingee) for that area and then i could use a GPS to add in points of intrest as i visit them as well as accurately put in any trails i followed or whack too. but that old tan colored map has my heart.

There are obvious differences between the maps. Makes for great reading. Only the TOPO map shows Thoreau's Bog. The AMC map and USGS show nothing. Also some of the bumps on Pumpelly Ridge seem more detailed on the USGS.

 

[DougPaul]

You might find the modern USGS topo useful (Mt Monadnock 1:25K quad). I looked for it on the Libre Map Project (http://libre.redjar.org), found the file name: o42072g1.tif, but they do not seem to have it available. My NG TOPO! suggests a date of 1984.

By way of background, the USGS contracted to have all topo quads digitized (DRGs--Digital Raster Graphics). (All sampled at 250dpi.) The data are public domain, but the USGS hasn't seen fit to put them on a server. Various states are available online at a variety of sites (used to be more, but commercial interests have gotten in the way...). I have some NH maps that I downloaded in 1999--if you had asked back then, I could have gotten the files for you...

Commercial sources: http://data.geocomm.com/, http://www.topozone.com, http://www.charttiff.com/, etc. One or more of these sites used to have the data available in a reduced sampling (lower dpi) version, but that seems to have disappeared.

BTW, a google search on "O42072G1" is interesting, but doesn't lead to any free data.

Doug

 

[Hillwalker]

Balloons

I seem to recall in some of my less retreivable memories an instance of hiking a trail that had numerous helium balloons tied to bushes for the purpose of determining the trail location in conjunction with aerial photographs. This was in the sixties, probably in Shenandoah National Park. The balloons were tied off just above the trees. They were also using what seemed like miles of orange thread that had been paid out along the trail. This was paid out using a reel with a counting device, and then retreived as scrap later. Memories of the days before microprocessors. I also seem to recall running across the temporary ground panels placed for aerial photography too. I love sitting down with a good map for some light reading. 1:24,000 rocks

 

[JOD]

NH gis site

starchild,

Good luck with the move after you're done and have some time look at this site NH GRANIT.

NH has an amazing GIS website. You can download topo maps and aerial images here. If you have the right software you can place the images in real world coordinate system. I use AutoCAD MAP for this. All GRANIT data are referenced to New Hampshire State Plane coordinates, North American Datum 1983 (NAD83). Units are feet. I use this source for work and play!

I also use Terrain Navigator Pro. This is also a commercial product used by the general hiking community for creating maps. You purchase the maps by region. I use New England for all my stuff.

For the gps I also use Garmin MapSource. This program allows me to upload and download maps, waypoints, routes, and tracks from the gps. I can export tracks and such to AutoCAD MAP and Terrain Navigator Pro.

I use these with my gps to record where I've been and plan where I want to go. I have the Garmin eTrex Legend. It works fine for my hiking needs. I don't refer to it while hiking just M & C.