But what was missing in my girls' education about the GPS unit was what the coordinates it displayed on its screen actually meant when they were translated to a printed map. A while back I made a map matching game and played it with a group of 4-Hers. We all had a lot of fun and learned quite a bit in the process (see below to take our Test Your Map Knowledge Quiz).
Part of the matching game included the term "confluence." That’s an exact spot where an integer degree of latitude and an integer degree of longitude meet, such as 43°00'00"N 71°00'00"W. Put another way, imaginary lines of latitude and longitude intersect each other, forming a grid that covers the Earth and helps us locate points on it. These imaginary lines are called confluences.
It’s a big (and key) mapping concept so I did of bit of research and found the Confluence Project website to help me explain this in terms of real life application to the kids.
This site posts trip reports of people documenting, through photos and their GPS units, confluences all over the world (and not all are on land - there’s water and ice cap confluences too). It’s a cool site (well maybe you sort of have to be a tech geek like me to appreciate it) and helped the girls understand what a confluence actually was and how we use these coordinates to pinpoint locations on a map (the Maine Gazetteer is also helpful since it displays confluences - and if you look really close at the 4-point or less type, you'll see coordinates on those lines as well).
After sifting through the confluences in Maine and New Hampshire on confluence.org (there are 64,442 possible confluences on the globe this site recognizes as do-able trip reports) we chose one that wasn‘t too far away and appeared easy to find. Well, it looked easy enough since it appeared to be off Route 302 just over the Maine border in Conway, NH.
It turned out that the 44° N 71° W confluence was in a swampy area in back of a private home. We did our best to get as close to the confluence as we could but we were .006 seconds off with our final reading.
But we learned (or in some cases, re-learned) some things:
- * Important map references can be in the most ordinary of places, like your own backyard.
* GPS units have a margin of error of 8-10 feet in most cases (newer models might be a little more accurate because the technology has improved tremendously in the past few years. My first GPS unit, about 5 years old now, had a margin of error of 30 feet.)
* The earth is always in motion so if you stop for more than a couple of seconds, your GPS unit coordinates will jump around. You may have been exactly where you were supposed to be but getting the GPS evidence of that can be tricky.
* Tree cover affects GPS units and how efficiently they can connect to satellites, which can affect your margin of error.
* Just because your GPS unit points you in a particular direction does not mean you throw common sense out the window and follow it (i.e., we weren’t going to trespass and/or walk through the mucky swamp any more than we had to - we learned this lesson a few years ago in Brunswick).
* Sometimes the effort of finding a place is more about the journey than the actual location. In the case of recording this confluence, Fino stepped through the snow and into the swamp. He was covered in mud up to both knees and that will be what is remembered by our family on this short adventure rather than finding the confluence.
Test Your Map Knowledge Quiz
1. The line of 0° longitude is called this.
2. Longitude lines give directions ____ and ____of the prime meridian.
3. The line of 0° latitude is called this.
4. Latitude lines give directions ____ and ____ of the equator.
5. There is another name for latitude lines. What is it?
6. What do we call the imaginary lines of latitude and longitude that intersect, forming a grid that covers the Earth and helps us locate points on it?
7. True or False: The Earth is a perfect sphere.
8. True or False: Each degree of latitude is divided into 60 min. and each min. into 60 seconds.
9. When you mark a point of latitude and longitude, what is that called?
10. Degrees of latitude and longitude are divided into 60 minutes. What is the symbol used to identify this?
(a) " (b) '
11. Degrees of latitude and longitude are divided into 60 min. and then those min. are divided into 60 seconds. What is the symbol used to describe seconds?
(a) " (b) '
12. If you set up your GPS unit to record and report decimal longitude and latitude, you would see which coordinates.
(a) N 43.917611, W -70.317695 (b) N 43° 55' 3.3996" W -70° 19' 3.702"
13. If you set up your GPS unit to record degrees, minutes & seconds longitude & latitude, you would see these coordinates.
(a) N 43.917611, W -70.317695 (b) N 43° 55' 3.3996" W -70° 19' 3.702"
(Questions 10-13 are important to understand when you own a GPS unit because these are setting options. And let me confirm that unless you are a geometry math whiz do not try to convert degrees, minutes and seconds to decimal degrees without a calculator. It’s not an easy computation. Geocachers use the degrees, minutes and seconds setting but Google maps defaults (at least in my experience) to decimal degrees so it‘s important when using a GPS unit to recognize that not all coordinate markings are listed in the same way. These two different coordinate settings in no way translates to the same location without the complicated geometry computation.)
ANSWERS to quiz are below photos
The swampy area was more easily managed at this time of year than it would have been if we ventured here in the summer. But Fino took a bad step and ended up to his knees in mud.
So close yet not quite for the true confluence.
Our closest reading caught on the camera of the confluence. Off by .006 isn't too shabby.
QUIZ ANSWERS: 1. Prime Meridian, 2. East and West, 3. Equator, 4. North and South, 5. Parallels, 6. Confluences, 7. False, 8. True, 9. A coordinate, 10. B, 11. A, 12. A, 13. B
No comments:
Post a Comment