On Sun, 1 Aug 2010, Nikhil Kaza wrote:
example(errorsarlm)
Right!
Or any other available dataset that mirrors the application case, which
seems to be ecological, but crucially has point or cell support in decimal
degrees with very large differences in distances between observations. You
are right that packages include lots of example data sets, and that they
are the place to start. In addition, the case is large, but the example
should not be, so that all the other problems can be eliminated first
before trying to scale up to moderate N (about 4000 if I recall
correctly).
The main problem is that the spatial process is conceptualised as
contagious in distance, and that the distance threshold is chosen to
ensure that all observations have at least one neighbour. This doesn't
seem helpful as many observations then have "too many" neighbours to make
sense. If the coordinates of the observations can be projected to the
plane, a graph-based neighbour scheme can be used, which represents the
spatial process as contagious in contiguity (neighbouring observations are
neighbours irrespective of distance).
So the first step is to think through how "neighbouring" observations can
influence each other in terms appropriate to the subject domain.
Roger
Nikhil Kaza
Asst. Professor,
City and Regional Planning
University of North Carolina
nikhil.l...@gmail.com
On Aug 1, 2010, at 7:57 AM, elaine kuo wrote:
Dear Dr. Bivand and list
Thank you for the patience.
Only one question remains
2. great distance circle
=> longlat = TRUE returns no valid observation ...
similar error messages have been researched in the archived mail
but no identical case found...
Please kindly suggest when longlat=TRUE,
whether the unit of both longitude and latitude is degree.decimal..
(confused with the manual explanation "measured in kilometer")
The threshold is in km when longlat=TRUE, but the coordinates are in
decimal degrees. Please state the representation of your coordinates - are
they in decimal degrees or not?
=> Yes, mine are in decimal degrees.
No, simply that you are including too many neighbours leading to too much
smoothing for many observations.
Please try everything on small examples until you understand what you are
doing. Best, use publically available small examples, and include complete
verbatim code (or post code on a website), max. 10 lines.
=> please advise any publicly available small examples to try errosarlm...
I have none at hand.. :P Thank you.
Elaine
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: roger.biv...@nhh.no
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