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Latitude, Longitude and the nautical Mile


Latitude, Longitude and the nautical Mile

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Dan Grim
Dan Grim
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Yup! Sorry to be the skunk at the party boys, but us GIS types are
movin' in.
We've done OK for years with one dbf file behind each of our GIS data
layers on our stand alone desktops, but as GIS becomes more and more sophisticated we are being forced into true relational databases. SQL Server being one option. I've just moved all of my 50-60 data layers into SQL server, running on the ESRI ArcGIS Server and ArcSDE platform. And having to learn SQL Server 2008 Standard from scratch is no small feat. Table joins, Indexing, Transaction logs, etc. Its all greek to us. So, give us a little time and allow us into your discussions. We need all the help you can send us.

The question of the day was quite a surprise. Thanks Steve for making us
feel welcome.
Steve Jones
Steve Jones
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Dan, you're welcome, but I had little to do with this. Someone else dropped it in there. I have written a few, but my knowledge of spatial data is low.

If you think there are some good learning questions, please feel free to submit them (use the Write for Us to the left). It would be interesting to see more spatial stuff. speaking of which, I have the Apress book on spatial that I need to get back to.

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Forum Etiquette: How to post data/code on a forum to get the best help
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Gary Varga
Gary Varga
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Isn't this just another example of how the RDBMS model can, not always should, be applied to different problem domains.

Welcome aboard Dan. As you can see from Steve's response, whilst each of us may be considered an expert in a particular area, none of us are experts in all areas. This is why we come here to share our knowledge, thoughts and experiences. Oh, in case you were wondering, I am just (?) a community member here.

Gaz

-- Stop your grinnin' and drop your linen...they're everywhere!!!
Tony Sollars
Tony Sollars
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Sorry - I might be missing something here - but isn't the answer wrong ...

The answer says - "There are 60 Nautical miles per degree of latitude, or one per minute of latitude. The length of a degree of Longitude varies from 60 nautical miles at the equator, to zero at the poles, so answer D would only hold true at the equator, not anywhere on earth. The answer is 'approximate' because the earth is an ellipsoid and not a perfect sphere, so there is some small variance in the length. "

Isn't it the degrees of latitude that get smaller approaching the poles? Hence - the answer would only be correct at the equator (ignoring the slight flattening around the poles..)

A definition of Nautical mile is - "A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet). ".

Meridians (i.e. lines of longitude) are great circles, but the equator is the only line of latitude that is a great circle.

Have I completely misread/misunderstood the question?
Gary Varga
Gary Varga
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Tony, I believe you are correct. I have already highlighted that they have answered the question if it referred to Sea Miles not Nautical Miles.

Hey-ho. I guess we will remember it a lot easier this way!!!

Gaz

-- Stop your grinnin' and drop your linen...they're everywhere!!!
Tony Sollars
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Thinking about it a bit more - it probably depends on how you describe what is being measured. Along a given line of longitude - measuring 1 degree of arc - is equivalent to measuring between X degrees latitude and (X+1) degrees latitude. Hence - it is the difference between degrees of latitude (providing longitude is constant.).

I was thinking the answer was implying measurement along a constant degree of latitude, e.g. from Y degrees longitude to Y+1 degrees longitude which does get smaller approaching the poles.

Hehe
mike brockington
mike brockington
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To those who are querying the answer, why not just follow the linked resource, oh, hang on, the reference is WikiPedia!? Double Fail then, first for the irrelevant question (this has nothing at all to do with the _operation_ of any database) and secondly for providing an unreliable source for the answer.

Throw away your pocket calculators; visit www.calcResult.com


SQAPro
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mike brockington (11/16/2009)
To those who are querying the answer, why not just follow the linked resource, oh, hang on, the reference is WikiPedia!? Double Fail


Pardon me your prejudices are showing. In most things Wikipedia is quite reliable and compares favorably with other resources such as Britannica. That's been old news since 2005 when Nature did their study, and it's been confirmed by a number of other studies since then. Look it up for yourself if you don't believe me
(http://www.lmgtfy.com/?q=how+reliable+is+wikipedia) (and yeah the top hit is wikipedia itsef, but hey, feel free to ignore the article content and just wade into the 100 linked references and do the research yourself if you don't trust wikipedia to host a non-biased article on its own accuracy)

Yes there's been problems, particularly in areas where there's incentives for people to provide false info, such as charged issues like politics, religion, or biographical information on prominent figures in such areas. But in matters of science Wikipedia has a good track record, and unlike other sources that may require a subscription, it's available for all and hence makes a good reference.

So unless you feel the actual content at the linked source (along with it's 12 linked references) is for some reason WRONG, don't dismiss it just because it's wikipedia.
Tom Thomson
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Steve Jones - Editor (11/11/2009)
It's a bit of trivia related to spatial information. If you work with data on the oceans, this can be valuable. It's not something most of us will deal with, but now it might stick in your head.



Stick in the head? No, next time I need to know I'll work it out again. (It must be a latitude delta not longtitude, since the distance is the same wherever one starts. The earth's circumference in nautical miles along a meridian great circle accurate to two significant figures is 22000 nautical miles (25000/1.151), is 1/(about 220000) full circles roughly 1 degree , one minute, or 1 second? It's one minute (60*360 = 22000 to two significant digits). End of story. So why should I want to remember the answer?

[edited to fix typos] [and again to fix a typo in "typos"]

Tom

mike brockington
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To be fair, WikiPedia itself warns on almost every page that some of the information provides no sources, and therefore is liable to removal. Assuming that there _is_ a verified source, then just link to that, then there can be no suggestion that the page has been altered merely to win the argument.
If no source is given, then the information is no more reliable than saying "it worked for me" or whatever.

Basically, quoting Wikipedia is a sub-clause of Godwins rule, or should be.

Throw away your pocket calculators; visit www.calcResult.com


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