Map reading and scales

[spider solo]

I've been trying to improve my map reading skills . I seem not to understand the WMNF scales on the AMC maps.
When I purchased a ruler for the various scales in common use
I find the maps are scaled 1:47500...one inch equalls 3/4 mile
the next map I turn to states
Scale 1:95000.....one inch equalls 3/4 mile
I recognize that one is double the scale of the other...so how can they both equall 3/4 mile ??

I know I can use string and this and that to figure mileage from a map, but I would like to have a better understanding of what the map info is trying to tell me.

Any help would be much appreciated........thanks

 

[sardog1]

A scale of 1:47,500 will result in one inch = 3/4 mile:
47,500 inches = 3958.33 feet = 0.75 miles.

A scale of 1:95,000 will result in one inch = 1.5 miles:
95,000 inches = 7916.66 feet = 1.50 miles.

Either the map has a typo or you're misreading a bar scale? (My maps are out in my truck, and fetching them right now would waken my wife.)

Maptools.com has free, scalable grids (and bar scales?) that are very handy. Pick your grid/bar and let your printer do the necessary resizing for you. Then take the output to a copy center and copy it onto clear plastic for a field-ready tool for any map you might happen to use. The site also has lots of helpful info on navigation generally.

 

[spider solo]

yes, seems to be printed error

As I check the maps each stating a scale of 1:95000.. one inch equals 3/4 mile.
However... now that I measure it... one inch does equal a mile and 1/2
Two inches equals three miles.

Just as you stated....so I would say the maps were released with that error printed on them.

The Presidental Range map ..scale 1:47500 seems ok..one inch equalls 3/4 mile. (4 inches equalls 3 miles)

Thanks for the maptools link I'll check it out seems like the way to go .
Nice idea to have the custom rulers made !

 

[Mark]

Maptools.com has free, scalable grids (and bar scales?) that are very handy. Pick your grid/bar and let your printer do the necessary resizing for you. Then take the output to a copy center and copy it onto clear plastic for a field-ready tool for any map you might happen to use. The site also has lots of helpful info on navigation generally.

Cool link - thanks! I esp. like the Latitude/Longitude Rulers.

If you have transparency sheets (for an overhead projector) for your printer, you can make map rulers yourself. If you don't already have some, it's probably cheaper to go to the copy center rather that buy a whole package of transparency sheets. One caution: if you have a water-based ink jet printer, these rulers will not be waterproof.

 

[carole]

While on the subject of map reading...

Looking at USGS maps many peaks (and other spots) have evelation marks but some have a 'T' after the elevation and others an "AT" (example 1910T or 925AT). Anyone know what the T and AT stand for?

 

[MadRiver]

My #5 Carter Range-Evans Notch map copyright 1998 also has a scale of 1:95000 and says one inch equals ¾ miles. Yet, one inch seems to equal 1.5 miles on the map.

 

[adkleaddog]

Looking at USGS maps many peaks (and other spots) have evelation marks but some have a 'T' after the elevation and others an "AT" (example 1910T or 925AT). Anyone know what the T and AT stand for?

Those are "spot elevations", not an actual benchmark, I don't think each one was actually measured by someone.

I asked this once from the USGS, it has something to do with how they derive the data, and come up with the elevations.... from some sort of mathamatical measuring system....I think

If you notice,some of the marks are in a grid type layout, they sort of match up in "boxes", sometimes....now you got me wondering again..I'll check!

 

[David Metsky]

There was a misprint on the first run of the new maps. You must have one of the incorrectly printed maps. It was corrected on the second run, but this was several years ago now. Is this an old map?

-dave-

 

[spider solo]

Sure enough.
I have various maps from the guide books over the years, though now I mostly use the Tyvek maps.
The one I have before me is map #3 & #4 from the AMC's White Mountain Guide, 26th edition..Copyright @ 1998.

Did they ever put out a notice of the error in the new edition ?

 

[Stan]

Did they ever put out a notice of the error in the new edition ?

Yes, when I purchased my Guide there was an errata sheet that mentioned the correction. All you need to do is write in the correct scale and the map otherwise is OK. On the other hand, you can leave it as it is and tell the Turtle Sisters, "This hike is only 10 miles, see, look for yourself."

 

[spider solo]

Yet another question...trying to plot coordinates from the map...AMC 27th edition Franconia Pemigewasset.... I notice the latitude lines go across nicely but when I line up the UTM lines the are all askew.

For example on the right side of the map the third blue tick UTM above lat 44 deg 10' reads 4895.
On the left side of the map the 1st blue tick has that reading.
If you draw a line across the map to connect the two readings it is a diagonal.
Which of course confuses me once again....?

Stan I like your idea...!!

 

[kltilton]

Yet another question...trying to plot coordinates from the map...AMC 27th edition Franconia Pemigewasset.... I notice the latitude lines go across nicely but when I line up the UTM lines the are all askew.

For example on the right side of the map the third blue tick UTM above lat 44 deg 10' reads 4895.
On the left side of the map the 1st blue tick has that reading.
If you draw a line across the map to connect the two readings it is a diagonal.
Which of course confuses me once again....?

Stan I like your idea...!!

The UTM lines are closer together at the top due to a concept known as convergence of meridians. Lines of longitude are closer together at the north pole than they are at the equator, they converge near the north pole. See sketch below.

 

[DougPaul]

Yet another question...trying to plot coordinates from the map...AMC 27th edition Franconia Pemigewasset.... I notice the latitude lines go across nicely but when I line up the UTM lines the are all askew.

The UTM lines are closer together at the top due to a concept known as convergence of meridians.

ktilton--you are referring to lat and lon in certain map projections. What you see on a piece of (flat) paper depends upon the projection.


The underlying problem is representing a section of a sphere on a flat piece of paper. UTM is a collection of mappings of small regions. From the center of each UTM region, extend north-south and east-west lines. Then each point in the region is represented by the distance from the NS and EW lines. The UTM grid lines are NS and EW at the center of the region but deviate at the corners.

The purpose of UTM is to make navigation easy in a small region by creating the fiction that each region is flat and using units of meters to locate each point.

Doug

 

[spider solo]

Yes I am surprised to learn that the UTM lines drift (or curve) on such a small map area... so connecting the UTM tic marks seems impractical.

Using the lon. and latitude lines would seem the better way to go...and could be further subdivided if desired.

 

[DougPaul]

Lat/Lon can be used to navigate in both large and small areas. However, calculating headings and distances without the help of a computer can be difficult (and counter-intuitive over long distances).

UTM (MGRS is very similar) was designed to make small area navigation simple and intuitive by viewing the world as a number of small flat zones. Local distance and heading calculations are easy. However, if a route crosses a zone boundary, it becomes difficult to use (without a computer).

A GPS, of course, contains a navigational computer (as well as the radio receiver for receiving the GPS signals).

If you would like to see some of the math, take a look at the Aviation Formulary: http://williams.best.vwh.net/avform.htm. (This formulary assumes a spherical earth--it gets even more interesting if you assume an ellipsoidal earth...)

Doug