Question on flow value CAT 'Time-Series Minimum Cost Flow'
Carlos Carroll
the CAT Google Group so others can reference it as well.
I will try and clarify the description of this function in the manual as
well.
The values recorded in the output text file are the outgoing flows for that
layer (eg, layer 1 of timestep 1).
You can see that because layer 2 in the last timestep has all values = zero
because there is no further flow to a later timestep possible.
Flow can be conceptualized as 'potential dispersal'. It is a function of
both the quality of the habitat and the supply of dispersers from previous
time steps.
So high quality habitat, if it is not isolated from sources of dispersers,
will have a high capacity to support dispersers and thus a high flow value.
This does not mean that dispersers will leave the site vacant in the next
timestep, as the arc/edge connecting a high quality site to the same site in
a future timestep also has a high value. Although this graph-based model
doesn't get into the complexities of individual behavior, you could
conceptualize the process as a proportion of offspring leave the site due to
the fact that the site cannot support all offspring. But a certain
proportion of offspring would remain at the site as well.
I don't believe you'd want to use the values in layer 2 of any timestep as
they are not directly related to the capacity of a particular site.
If you read through the Phillips et al. 2008 paper that might also be
helpful.
Let me know if you have any other questions.
I'd like to learn more about the maps of results you sent, what type of cost
layer are you using?
If I am interpreting your problem correctly, habitat shifts eastward between
time steps 1 and 2 but the intervening area has high cost.
This problem may have more parallels to some of the work in Phillips et al.
2008 than to the examples I include in the Toolkit Manual.
" I am a master degree student from the geography department of National
Taiwan University.
I tried to use CAT to perform a spatio-temporal analysis of habitats change.
In the 'Time-Series Minimum Cost Flow' method, in the Toolkit Manual, it
says that the output files contain the hex_id and outgoing flow values.
What does outgoing flow value mean?
. If it means the value of flow out of the
hexagon, why those hexagons with high habitat
value have a high outgoing flow value?
(i.e. if the hexagon is a good habitat, why do
animals move out?)
. I think 'outgoing flow value' should mean the
value of flow into the hexagon. Am I right?"
_____
Carlos Carroll, Ph.D.
Klamath Center for Conservation Research
PO Box 104
Orleans, CA 95556