On 15-Apr-04 Mark Coleman wrote: > ... In particular, I have been using a small test data set > provided by Anselin on crime data in Columbus OH. Each sample point > includes a lat-long coordinate. The data set can be found at > http://www.spatial-econometrics.com/data/ > > As an example, the first point in this data set shows latitude=35.62, > longitude=42.38. Yet when I check the coordinates of a random point in > Columbus OH (not in the dataset), I find coordinates in the range of > Lat=40.x, Long= -82.y.
Well, clearly either there's something seriously wrong with the data (35.62 deg N 42.38 deg W is in the middle of the Atlantic, 35.62 deg N 42.38 deg E is on the Iraq-Syria border) or things are different from what one might first think they are. According to the file http://www.spatial-econometrics.com/data/anselin.txt we are only told that % column4 = latitude coordinate % column5 = longitude coordinate but we are not told the units nor the origin. Have a look at the numbers in http://www.spatial-econometrics.com/data/anselin.dat min(lat) = 25.25, max(lat) = 51.24 min(long) = 24.95, max(long) = 44.07 Now, 1 degree of latitude is about 60 miles, so if these were degrees then you're looking at a range of some 1,500 miles N-S; similarly (though less) for E-W. Even Ohio ain't that big! So I suspect that we're looking at minutes of arc rather than degrees, relative to some fixed point. One minute of arc in longitude is about 1 mile, so you're now looking at about 26 miles N-S. At the latitude of Columbus (35.62N), 1 minute of arc is about 0.66 miles, so you're looking at about 11 miles E-W. Also, it seems that the precision is 0.01 minutes of arc, or about 18 yards (N-S) by 12 yards (E-W). This all looks plausible ... Hoping this helps (and wondering if I'm right ... pity people don't document this sort of thing properly in their data files; it would only have taken a line to do so.) Best wishes, Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <[EMAIL PROTECTED]> Fax-to-email: +44 (0)870 167 1972 Date: 15-Apr-04 Time: 17:52:40 ------------------------------ XFMail ------------------------------ -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
