xhy your questions are long-standing and as yet unanswered in general.
> 1. How to select the lag class and lag distance in > order to obtain a more reasonable experimental > variogram? I always think of it as focussing a camera. Believe there is a pattern in your data and our task is to balance 'width of interval' versus 'number of pairs in interval' to get the clearest picture. One of the things I have found most useful with irregularly spaced data is a 'nearest neighbour' analysis. Take each sample and find the closest one to it. Record the distance. Repeat for all samples. This process takes twice as long as calculating the semi-variogram but gives you an idea of the 'natural' or model spacing between your samples. This can be used to guide your choice of interval. Check out our free tutorial downloads at http://geoecosse.bizland.com/softwares > 2. Is it reasonable to use an uneven set of lag > (e.g. the lag increments are: 0-2.5m, 2.5-5.0m, > 5.0-12.0m, 12.0-19.5m, 19.5-27.0m, 27.0-30.0m, > 30.0-40m, 40-50m etc.) if a more stable variogram > can be obtained? I am not sure I have ever seen this done, but don't see why not if you plot the point at the centre of gravity of your interval (i.e. average distance of pairs found). Hope this helps Isobel http://geoecosse.bizland.com/books.htm ___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com
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