Juliann Three obvious possibilities:
(1) you have a large scale trend which only shows up when you start taking pairs at larger distances. This would be the case if your second 'rise' tends to curve upwards rather than flattening. (2) you have anisotropy. If you did an 'omni-directional' semi-variogram, your smaller distances will have pairs from all directions and you will see an 'average' sort of semi-variogram. When you go to larger distances you are getting lots of pairs in whatever direction lies between the two clusters and not much in any other direction. So your larger scale semi-variogram may be the one in that direction only. (3) you are actually dealing with two different population groups within the sampled areas. If they have much the same internal structure but differ from one another in behaviour, you would get this type of behaviour. In geological applications, you would look (perhaps) for a fault line or geological boundary between the two. As Pierre says, you must ask some basic questions. Mine would be: why were those two areas so heavily sampled with comparatively sparser sampling elsewhere? Hope this helps Isobel http://uk.geocities.com/drisobelclark __________________________________________________ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- * 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
