View Full Version : Dumb question about reading maps
Jeanette
01-30-2006, 20:55
So when you're looking at an elevation profile, does the mileage scale at the bottom give you the mileage "as the crow flies"? Or does it take into account the ups and downs that you encounter as you make your way from point A to point B? If your elevation changes a lot, it would be a potentially significant difference in mileage, compared to if you went straight from point A to point B on a flat plain, right?
I can't believe I've been backpacking for 14 years and am still a really lousy map reader.
I thought it would be less embarrassing to ask this question of a group of women rather than endure the virtual male eye-rolling that I might encounter elsewhere. ;)
I would say that if it is an elevation profile that it would be taking into consideration the ups and downs.
johnny quest
01-30-2006, 21:28
the distances you see on the map legend scale are "as the crow flies." experience and training....and more experience will teach you to estimate actual distances. very very very often the closest route doesnt lie in a straight line, but in a less extreme contour.
All distances on a map is as the crow flies. Profiles dont always tell the story so learn to read the contours and enjoy what comes your way, for every up there is a down.
The distance on a map is the horizontal distance, as the crow flies. That does bring up an interesting question, since I gather the total length of the trail was measured by a wheel so would be the true distance. I wonder whether the distance on the profile map is made from that measurement or from measureing the trail as laid out on the map, or is some other system used?
:-?
The elevation profiles also show distances (on the bottom) in trail miles, not as the crow flies. For instance reading the profile and the corresponding mileage below it will give you trail miles from Point A. Or lets say, on your NH map, it's 5.7 miles from Mt Washingon to Madison Hut on the profile, same as your guidebook. The bumps inbeween also reflect trail miles.
The "dumb" questions are the ones you have but don't ask.
If you went from Mt Washington to Osgood you obviously wouldn't get mileage as the crow flies on the profile map. Sure you could use the scale on the topo and adjust for elevation changes but the profiles already to that.
fiddlehead
01-30-2006, 22:02
you can use a piece of string to get a better idea as the trail curves on the map. But every turn isn't going to be on there so it won't be entirely accurate but you can get a much better idea that way. Just lay the string on all the turns on the trail on the map, then straighten out the string and put it next to the scale at the bottom of the map, and you'll have a better idea of how far it is.
There are other tricks like this, but the best way to learn is just go out there and experience it and experiment. Map scales can mean a lot. For instance, i know that on a 100,000 to 1 scale, One inch is aprox. one mile. But again, you must compensate for the map maker not putting every turn on there. Use common sense and it'll come to you. good luck, and have fun.
Alligator
01-30-2006, 22:11
...For instance, i know that on a 100,000 to 1 scale, One inch is aprox. one mile. ....
Sorry to interupt, but this needs to be pointed out. A 100,000 to 1 scale means that every inch on the map measures 100,000 inches on the ground. 100,000 inches~8333 ft~1.57 miles.
Sorry to interupt, but this needs to be pointed out. A 100,000 to 1 scale means that every inch on the map measures 100,000 inches on the ground. 100,000 inches~8333 ft~1.57 miles.
Only if the unit of measure is an inch. If you shrunk a 1:100,000 map down 50% the unit of measure would be .5" which would equal 1.57 miles.
Alligator
01-31-2006, 00:26
Sly, we were talking about maps not reduced/enlarged photocopies of maps. The statement 1:100000 indicates a representative fraction.
http://geography.about.com/cs/maps/a/mapscale.htm
As another example, one centimeter on the map indicates 100,000 cm on the ground. 100,000cm=1000m=1 km. It's probably what Fiddlehead was thinking of.
RF and verbal scales (one inch=mile) are not maintained in reductions/enlargements, while graphic scales are.
I actually did the 1 inch to 100,000 inch calculation before I looked up the link BTW;) .
Sly, if you shrink a 1:100,000 scale map down 50% it becomes a 1:200,000 scale map.
The "dumb" questions are the ones you have but don't ask.
And the dumb answers are answers that are wrong. The mileage figures on the profiles on the Maine Maps produced by MATC are trail miles, not "as the crow flies" miles -- I think. Well, actually I'm quite sure. Actually, I'm positive -- almost anyway.
Weary
I'm getting a little confused but it sounds like, six of one, half dozen of the other! ;)
Sly, if you shrink a 1:100,000 scale map down 50% it becomes a 1:200,000 scale map.
I'm not sure of that... to wit.
RF and verbal scales (one inch=mile) are not maintained in reductions/enlargements, while graphic scales are.
Since the graphic scale is maintained, if I reduce the map 50% the *1* in 1:100000 becomes .5" yet the detail of the map remains the same, only smaller.
So when you're looking at an elevation profile, does the mileage scale at the bottom give you the mileage "as the crow flies"? Or does it take into account the ups and downs that you encounter as you make your way from point A to point B? If your elevation changes a lot, it would be a potentially significant difference in mileage, compared to if you went straight from point A to point B on a flat plain, right?
It's a good question. The answer depends on how the distance was measured. If it was measured by pushing a bicycle wheel, then you have the actual over the ground distance. If it is measured by survey methods or using a GPS, then you have horizontal distance. Regardless of which way it was measured, there really isn't significant difference between the two methods. The map profiles are very exaggerated. I could run through the numbers, but it isn't as big as you would think it should be.
profiles lie. use the map for water, shelter, campsite locations, and road crossings. as far as mileage, just hike until you get there. for me, looking at a 1000 foot climb on the profile, thats obviously gonna whip my a**, is detramental to my mind set.
Rain Man
01-31-2006, 09:44
I suggest you contact the map man at the ATC. Can't remember his name just now, but he's a nice guy and would be happy to answer this very good question. Just call or email the ATC. If you do, please share the answer!
I think I know the answer, but don't want to be guessing for you. Others have been guessing already, obviously.
Rain:sunMan
.
Tha Wookie
01-31-2006, 10:17
The elevation profiles also show distances (on the bottom) in trail miles, not as the crow flies. For instance reading the profile and the corresponding mileage below it will give you trail miles from Point A. Or lets say, on your NH map, it's 5.7 miles from Mt Washingon to Madison Hut on the profile, same as your guidebook. The bumps inbeween also reflect trail miles.
This is correct for the AT. It is not "as the crow flies", but a cartographical interpretation of the wheeled milage on the ground and the topo characteristics. Obviously, some peaks and gaps have "true" measures, from a variety of techniques, the in between is educated guesswork. -that's why it sometimes it feels way off.
Also, Alligator is right about the distance. The statement 1:100,000 expresses one map inch for 100,000 inches, as the crow flies. You still need to factor in the topo lines. Also, be careful as some parks use the metric system, where 1:100,000 expresses units of measure in centimeters instead of inches. Always check the legend to be sure when doing backcountry navigation.
EXCELLENT QUESTION!;)
Footslogger
01-31-2006, 10:21
All the above reasons are why the Elevation Profiles are a helpful indication of trends in terrain. However due to the plotting scale they "smooth" out a lot of the ups/downs we as hikers experience while actually walking the trail.
I've cursed many an Elevation Profile in my day.
'Slogger
icemanat95
01-31-2006, 10:57
All the above reasons are why the Elevation Profiles are a helpful indication of trends in terrain. However due to the plotting scale they "smooth" out a lot of the ups/downs we as hikers experience while actually walking the trail.
I've cursed many an Elevation Profile in my day.
'Slogger
People allow themselves to get psyched out by the profiles rather than just using them and interpreting them. They are HIGHLY exagerrated, sometimes by as much as a factor of 7 to 1....that's a lot of verticle exageration. They are never as steep as they look on the profiles. Once you understand that, it gets easier to deal with them.
Yes they miss the odd up and down. If the elevation change is less than the map contour scale can resolve, or the trail path on the map misses a jog that would cross a contour line, then that elevation change will be lost, but I never found the profiles to miss elevation changes of more than say 10-20 meters, which is only 40-80 feet, and that's an extremely high scale since most of the maps are scaled to 3 meter contour lines, or about 10 feet.
Extra distance resulting from elevation is probably not all that significant except where the grade is severe. If you rise in elevation by 1000 feet over the distance of one mile, the additional distance covered as a result of the elevation is less than 100 feet. There are very few places on the AT with elevations steeper than that. You MIGHT experience an extra mile of distance as a result of elevation changes, over the course of a day.
The formula is simple, the subtract the trail miles (converted to feet) as listed, from the result of the square root of (A squared (the trail miles in feet) + B squared (the elevation change in feet)). OK, finding square roots isn't simple for most of us, but a calculator will handle it nicely. It's just not going to be very significant unless you let your head get wrapped up in it.
Don't psyche yourself out.
Footslogger
01-31-2006, 10:59
The formula is simple, the subtract the trail miles (converted to feet) as listed, from the result of the square root of (A squared (the trail miles in feet) + B squared (the elevation change in feet)). OK, finding square roots isn't simple for most of us, but a calculator will handle it nicely. It's just not going to be very significant unless you let your head get wrapped up in it.
Don't psyche yourself out.
===================================
Nah ...I'd rather psyche myself out. Gives me something wrap my head in.
'Slogger
Kerosene
01-31-2006, 11:59
It's interesting that out of the 23 responses to Jeanette's posting to the Female Hikers Forum, at least 20 of them are from male engineering types, many of whom can't agree with each other. You're the one who should be rolling your eyes, Jeanette!
johnny quest
01-31-2006, 12:11
amen! we are a bunch of idiots arent we? but in my defense i have to say i had no idea i was in the womens forum until now. i just came to this thread from the home page highlights.
So when you're looking at an elevation profile, does the mileage scale at the bottom give you the mileage "as the crow flies"? Or does it take into account the ups and downs that you encounter as you make your way from point A to point B? If your elevation changes a lot, it would be a potentially significant difference in mileage, compared to if you went straight from point A to point B on a flat plain, right?
I can't believe I've been backpacking for 14 years and am still a really lousy map reader.
I thought it would be less embarrassing to ask this question of a group of women rather than endure the virtual male eye-rolling that I might encounter elsewhere. ;)
its not a dumb question:cool: neo
Alligator
01-31-2006, 12:41
First, I have to clear another point. When it says 1:100,000--a representative fraction scale--this is unitless. It doesn't matter if you use metric, english, or any other units of measure for length. It matters if it is a verbal scale and we say one inch=10 miles or 1 cm=1 km. Then the units are critical.
...
Since the graphic scale is maintained, if I reduce the map 50% the *1* in 1:100000 becomes .5" yet the detail of the map remains the same, only smaller.
Sly, did you read the link I sent? The one doesn't change to a .5 in the photocopy, it only prints smaller:) .
Consider a 2"x2" map. There is a graphic scale and a representative fraction of 1:100,000. That means that on the ground, the map represents a square 200,000X200,000 in. If I reduce it 50%, the map will be 1"x1". That 1" now represents 200,000". The scale has been changed to 1:200,000, as Map Man stated. Yet the text on the map will still say 1:100,000 and is therefore incorrect. The graphic scale will remain true, as long as it was also included in the reduced copy.
If this is not sufficient, please either PM me or start a new thread outside the women's forum.
Jeanette, I've been meaning to find an answer to your question for some time.
bulldog49
01-31-2006, 12:53
I don't have access to a map here at work but there is a very simple way to prove who is correct.
If the space between each mile marker on the contour map is the same, then the distance is as the crow flys, ie, equal to the distance on a regular map. If the space varies, then it is trail miles. My recollection is the spaces are the same and are as the crow flys.
Gray Blazer
01-31-2006, 13:00
Do what my wife does. Stop some man and ask him. She has no faith in my map reading skills and is always amazed when we make it to our destination on time.
Jack Tarlin
01-31-2006, 13:16
Some good advice here.
What the profiles are best for is to give you an approximate (in some cases, tho, it's a quite accurate!) picture of the Trail lying ahead of you.
This is a great aid when you're planning your day's hiking, or wondering how far you'll get, or where you'll likely be at the end of the day. Most hikers hate to have a monster climb at the end of the day, preferring to do the toughest climbs early in the day, when they're fresh, and before it gets too hot. Very few folks want to deal with a 3,000 foot climb at four-thirty after they've already done thirteen miles!
This is where the profiles will really come in handy. They'll show you when you might want to go for a big-mileage day, and will also show you where this might not be a good idea. If you want to finish the day with a climb to maybe catch a nice sunset, the profiles will show you this as well.
A lot of folks complain about the profiles, especially as regards their accuracy. (It is indeed true that sometimes, the roughest days will include tons of nasty little ups and downs that don't look much on the profile!) I've found them to be very useful over the years, tho. Some hikers say they don't want to know if there's a big hill ahead of them, or a tough day's hike: Their feeling is that they've got to hike the section anyway, and they don't want to spend a whole day dreading what's waiting for them up ahead. For me tho, I'd rather know, as it helps me plan my day, and my mileage, accordingly.
The Old Fhart
01-31-2006, 20:44
There is some confusion here. The map and the trail profile are entirely different ways of presenting the physical world.
First, the earth is a sphere, but if you could cut the earth into segments(like orange slices) then flatten these strips(peels) you would get what maps represents. There is some intentional distortion introduced because the orange peels segments from the slices when flattened are wide in the middle(equator) and come to a point at each end(north and south poles) and these can’t be cut into nice neat rectangles. In the northern hemisphere the cut up areas would be trapezoidal, narrower at the top (north) side, but they are “corrected” (Google “map projection”) to rectangles to make them easier for us to use. The A.T. maps would represent a very, very small area cut out of a flattened slice. This area when viewed from a great distance above is 2-dimentional, that is, the area is as flat as the paper it is printed on. If you look down on the earth below from an airplane at 35,000 feet you know what I mean. Any distance measured on the map is therefore a straight line, as the crow flies distance because there is no elevation. The contour lines and printed elevation values on the maps helps you to visualize the missing elevation element on the flat map.
The trail profile on the other hand is simply a graph with a linear mileage (horizontal) scale so each and every division represents the same distance. If we were to walk the A.T. with a measuring wheel and every mile (or 1/10, whatever) stopped and took an elevation (vertical) measurement, we could plot these distance vs. elevation readings and produce a trail profile. Note that the same scale isn’t used for the horizontal and vertical. If you look at the A.T. trail profiles you will see that it says something like “vertical exaggeration 5.28” to one, or something like that. The reason for this exaggeration is to make the profile more meaningful and easier to understand.
If you had a very narrow straight mountain range with gaps and peaks and a trail running end to end, you could slice vertically through from top to bottom and get a physical profile like the mountain silhouettes you see at sunset. If you took a measuring wheel and at each measured trail mile along this edge you drew a paint line straight down from where you were to the base line you would get a horizontal scale that would vary like a Slinky between mileage divisions and be very hard to understand. That is why this method isn’t used.
For all its inaccuracies I often found the profile the most useful part of the map. Partly for its depiction of ups and downs but more because it showed the Trail stretched out in a straight line, showing graphically the distances between shelters, corssings etc. That made visualizing the landmarks ahead easier than by looking at the map or a mileage table. Since most of the trail is clearly marked, I found the information not on the profile not as frequently used as the information on it.
[giggle] Too bad I cut most of the profiles off while trimming down the map margins to save that last tiny bit of weight! The only ones that survived were the ones with map of the trail on the reverse side of the part with the profile. The good part was that getting each new map from my bounce box was like opening Christmas presents, wondering if this one would have a profile still attached.
:sun
Next time I might be tempted to bring ONLY the profiles except for sections like the Whites. But since I am addicted to maps I will probably leave them uncut.
sliderule
02-01-2006, 19:46
The statement 1:100,000 expresses one map inch for 100,000 inches, as the crow flies. Also, be careful as some parks use the metric system, where 1:100,000 expresses units of measure in centimeters instead of inches. ;)
With regard to the map scale, it makes absolutely no difference what unit of linear measurement is used, provided that the same unit is applied to both sides of the ratio. It does not matter whether the unit of measurement is centimeters, inches, feet or meters, etc. 1x on the map equals 100,000x on the ground. (Horizontal measurement not adjusted for vertical variations in topography.)
Here is a scale question: Which is a larger scale, 1:50,000 or 1:100,000?
fiddlehead
02-02-2006, 04:51
I'm not an "engineering type" that i know of but do now that when i'm using a 100,000 to 1 scale map. And i use my thumb and 1st and second fingers tightly together (which equals one inch in my case) I can use this form of measuring (sounds a bit crude but it works) to figure out from the map how many miles it is to somewhere i'm going or somewhere i've been.
I showed this little trick to lots of folks on the PCT when i hiked it and many were using it to figure out mileage.
I guess i should be glad that none of them were engineering types because no one told me it didn't work that way. (probably because they saw for themselves that it did!)
so, sorry if i mislead anyone here. The system i was trying to describe is one i have used so many times on 100,000 scale maps. (they used to be the norm although who knows what the norm is now with all the computer generated maps.)
Anyway, the string laid across the winding trail will perhaps be a little more accurate (straighten the string out and hold it next to the scale at the bottom) but the thumb and 2 fingers trick works great for a quick estimation.
Perhaps those who are disagreeing with me on this should go out there and try it first.
Call me whatever you like, it bounces off, but i'm trying to help the 1st person on this thread who asked the question. not the jerks who are knitpicking my system apart!
Chef2000
02-02-2006, 06:23
throw the maps out. I hiked the entire trail just using the data book and Companion.
throw the maps out. I hiked the entire trail just using the data book and Companion.
Not a responsible thing to do.
Not a responsible thing to do.
But please argue on another thread somewhere else?
[quote=Alligator]
Sly, did you read the link I sent? The one doesn't change to a .5 in the photocopy, it only prints smaller:) .
Yeah <deleted answer> back to re-thinking
Pedaling Fool
02-02-2006, 19:38
Short Answer: Yes, the mileage on your profile is the mileage you walk.
Reason: Your map is on a scale of 1:63,360 or 1 inch = 1 mile (Note: This scale is Horizontal distance ONLY).
If the map-makers applied that same scale to vertical distance, you would hardly see any "ups and downs" on the elevation profile. Therefore, they exaggerate the vertical distance; hence the term "Vertical Exaggeration" that you see on your map.
Remember, the highest point on the trail is a little over one mile high, that would be only about 1" in height, if put on the profile sheet at 1 : 63,360 ratio, therefore they exaggerate vertical distance.
Lots of people say you dont even need the maps on the AT and, with the blazes and maintanence, that is probably true. The thing is, though, it is a great place to learn how to read a map and get map and compass skills in a relatively safe environment and then transfer those skills to other places where they may be more important, such as the CDT
Sly, if you shrink a 1:100,000 scale map down 50% it becomes a 1:200,000 scale map.
or 1/2"= 100,000 assuming an accurate 50% reduction.