Friday, December 12, 2014

Answer: Finding the measures of things

Vernal Fall in Yosemite 
This week's Challenge was intended to get us thinking about the questions.   As many of you correctly pointed out, even questions that sound simple often have a certain amount of ambiguity in them.  

You learn this very quickly when you're a Reference Librarian sitting at the Reference Desk.  They're the people in the library (or online, as in the "Ask a Librarian" service) who answer your toughest reference questions.  They get hit with some questions like the ones I asked in the Challenge.  Prototypical questions might be: 

  • Why was the Civil War fought? 
  • How deep is the Grand Canyon? 
  • Who won the War of 1812? 
  • I can't find War & Peaches. What's that book all about anyway? 
As you see, you can't just flat out answer these questions.  At the reference desk, the ref librarian conducts a reference interview to figure out what the asker really wants to know (and how much they'll understand).   "Why was the Civil War fought?"  Great question. Just saying "slavery" is inadequate.  Instead, the librarian will talk with you--what do you really want to know?  The economic conditions?  The history of abolition?  Political tensions between the states?  

Likewise, answering "how deep is the Grand Canyon?" and "Who won the War of 1812?" depends a lot on where you stand and how you take the measurements. 

Of course, War & Peaches is really a mondegreen of the Tolstoy book title, War & Peace.  

So it goes with our questions from the Challenge.  They were:  

1.   What is the elevation of Vernal Fall?
2.  What is the distance to Jupiter?   
3.  How big is a 2x4 ("two by four") piece of wood?  

The ambiguity of the questions becomes pretty evident once you start to look for the results?  

1.  "The elevation of Vernal Fall?"  Well, tell me what you mean by "elevation"?  Is that the altitude above sea level of the top... or the bottom of the falls?  Or could you mean the distance the water falls from lip to base?  

If you do the obvious query to Google, you'll get a result that looks like this: 

You have to read this result carefully.  Note that the search term "elevation" is bolded in the result snippets.  It's a big hint that elevation might not mean what you think it means.  If you click through the first couple of results, it becomes clear that "elevation" here means "height above the Yosemite Valley floor."  The number (1,014 m) is extracted from a number of web pages that are hiking guides.  For that purpose, "elevation" is a good number to indicate how difficult of a hike it is.  

Now if you thought "elevation" meant "altitude," you'd be completely misinterpreting the result.  

Unfortunately, if you do a more precise query [ altitude Vernal Fall ] you'll still get the same answer because Google synonymizes "elevation" and "altitude."  See? 

Note carefully what it says in grey text below the number:  "Vernal Fall, Elevation" 

Of course, that's not what you intended.  You asked for "altitude"  

If you want the altitude of the top (or bottom) of the Fall, you'll need to look at a map or find a guide to Vernal Fall that gives it to you explicitly.  

The official National Park Service Yosemite Valley Map shows that the Falls are at 5044 feet (1538 m).  But is that the top or the bottom of the falls?  

To REALLY check on things like this, I always look at the topographic map.  (Search for [USGS topographic maps ] and use their system to search for the map of Yosemite Valley.  It's called "Half Dome" for the famous semi-dome nearby.) 

When you find that map, the relevant piece will look like this: 

See that elevation line at 4800?  It's one heavy line below the top of the Fall.  (Trace it with your finger.)  The legend at the bottom of the map says these lines are 200 feet apart.  So the heavy elevation line that passes just below the top of Vernal Fall is 5000 feet.  So the NPS map's number (5044 feet; 1538 meters) checks out.  

2.  "Distance to Jupiter?"  Well, tell me what you mean by "Jupiter"?  And then tell me what you mean by "distance"?  

It seems silly to ask "what's Jupiter?" but don't tell that to the citizens of Jupiter, FL.  If you're in Talahasee, FL, "what's the distance to Jupiter?" probably means "how long will it take me to drive to the town of Jupiter!"  

So you have to be impressed when the answer from Google to the obvious query is this:  

As the first answer box points out--the distance from Earth to Jupiter varies day-by-day.  If you read the result carefully, it says "at their closest.." they can be 628,743,036 km apart.  But what about at their farthest?  I'll let you look that up, but it's a long way from one side of the solar system to the other.  The distance changes moment-by-moment.  

Of course, the other interpretation could be "how far is Jupiter from the sun?"  If that's the real question, then you have to ask "do you want the distance from surface of the sun to the surface of Jupiter?"  or do you just want center-to-center?  The site puts Jupiter (center-to-center) at 5.2 AUs (Astronomical Unit, which is 1 Earth-t0-Sun distance of 93M miles).  So from Sun-center to Jupiter-center is around 483M miles (777M km).  

3.  "How big is a 2x4 piece of wood?"  Well, tell me what you mean by "big"? 

Usually people think of a 2x4 as a standard measure.  As Wikipedia tells us in the article about lumber: "...a "2x4" board historically started out as a green, rough board actually 2 by 4 inches (51 mm × 102 mm). After drying and planing, it would be smaller, by a nonstandard amount. Today, a "2x4" board starts out as something smaller than 2 inches by 4 inches and not specified by standards, and after drying and planing is reliably 1.5 by 3 .5 inches (38 mm × 89 mm). It is made to absorb natural variation."

This is backed up by the article on Wood Sizes from the site, which also points out that lumber sizes vary depending on if its softwood (e.g., pine lumber) or hardwood (e.g., oak) that's being measured.  
Of course, there's the issue of length.  The actual weight (or volume) of a single 2x4 can vary tremendously depending on length.   In the United States and Canada the standard lengths of 2x4 lumber are 6 feet (1.83 meters), 8 (2.44), 10 (3.05), 12 (3.66), 14 (4.27), 16 (4.88), 18 (5.49), 20 (6.10), 22 (6.71), and 24 feet (7.32 meters).

The upshot is that a "2x4" is actually smaller than the term would suggest, and the largest variation is size (that is, "how big it is") depends on its length--from 6 feet up to 24 feet.  

Search lessons:   

Like a great reference librarian, when you're searching, you really want to understand the question that is being asked.  You have to take into account the variation in what the original question statement is, and the variation in what your reference materials (including Google!) can tell you.  

As we see in the Vernal Fall elevation example, you must read the content carefully.  This is probably the single biggest source of mistakes I see in students.  Even if they frame the search carefully and correctly, but then misread the results, then they're still wrong, even though they did everything right up until the last step.  

One way to avoid this problem is to double-source everything.  I've done that in these examples, and it's a great practice to do.  (But be wary of duplicates in the results.  If you're seeing the same language multiple times, start digging more deeply.)  

Search on!  

(And read those results carefully!!!)  


  1. good point/reminder about reeding context cautiously… ;_-]
    thanks for the cogent explanations and tools.
    reminds me of these kind of instructions from my paleo-education indoctrination days (Mr. Clark's math/life class - still view him flying the Po Valley looking for Tigers)…

    this might be a Jupiter for you.
    in FR or NL

    serendipitous tie to recent water/67P/Churyumov–Gerasimenko (it is a Jupiter-Family comet) posts -
    ESA - if there had only been more power…or harpoon action
    Kuiper Belt
    Kuiper background

    not to be overly nit picky, but the topo I looked at showed 40' intervals in the legend - seems to make more sense…?
    "See that elevation line at 4800? It's one heavy line below the top of the Fall. (Trace it with your finger.) The legend at the bottom of the map says these lines are 200 feet apart. "

    interesting example and worth noting Hans's longevity in searching, sorting and sensemaking…
    "Following the oil strike at Drake Oil Well in Pennsylvania in 1859, there was a short-lived oil drilling boom in California, but this was wiped out in 1867 when eastern oil could be sold cheaper. At the end of the first boom, 75 companies had drilled 60 wells in California, spending $1 million to produce $60,000 worth of oil"
    Pico Canyon
    1st prohibitive well

    ⌘-F 2x4 - it's in the comments

    fwiw: another example of failing to read/follow directives… re: photospheres - for whatever reason they show "no data available" however street view points along the trail come up…¯\_(ツ)_/¯
    Mist Trail photosphere - inactive
    Mist Trail Pegman - active
    a Yosemite view

    enjoy the sky water… in all its forms - hopefully no scuba @ the GPlex!
    Jupiter related ♫♪♭♩ to read by
    cola & winstons - celestial
    Gustav Holst
    another non-visual way to "look" at the Planets

  2. About the distance from the Earth to Jupiter. Hans, Ramón and jon were right in their answers: minimum distance is about 588.5 million km (that's on the quoted NASA's Jupiter Fact Sheet).

    The 628,743,036 km figure stands for the mean value at "minimum distance position" (opposition from Earth, that is, when the Sun, then the Earth and then Jupiter stand in a line).

  3. Hello Dr. Russell and everyone.

    Challenge was very interesting, with new tools, lessons and with lots of fun and new facts.

    I didn't know about Jupiter, FL.
    Double-source is a great advice to add to my list.

    I searched for "elevation" but couldn't find what those numbers meant. Until I read your answer :" "elevation" here means "height above the Yosemite Valley floor." The number (1,014 m) is extracted from a number of web pages that are hiking guides. For that purpose, "elevation" is a good number to indicate how difficult of a hike it is. "

    I liked too the topographic maps explanation and how you used as a verification tool.

    Finally, thanks for the reading carefully and seeing same language tricks. Many times, I forget to read twice and that causes issues. Also, I will read it again to learn better.

    Have a great weekend.